Does Zen have an unusual view of samadhi?

but fundamentally it is unity with the whole universe

In light of Alagaddupama Sutta, this does not fit with:

‘The self is the world; after death, I will be permanent, everlasting, eternal, unchanging in nature, eternally the same; I will endure as long as eternity’—this, too, he regards thus, ‘This is mine; this I am; this is my self.’

Alagaddupama Sutta

Seated thus at one side, he said this to the Blessed One: “Venerable sir, it is said, ‘Right view, right view.’ In what way, venerable sir, is there right view?”

“This world, Kaccāna, mostly depends upon a duality: upon (the notion of) existence and (the notion of) non-existence.

But for one who sees the arising of the world as it really is with right wisdom, there is no notion of non-existence regarding the world.

And for one who sees the ending of the world as it really is with right wisdom, there is no notion of existence regarding the world.

Kaccā(ya)na.gotta Sutta

I shall be no part of all the world.

Atammaya Sutta

Which might lead to eternalist view. The above statement makes the link of "thatness" with the universe. Ultimate reality is neither that nor this. But causality gives the notion of "this" dependent on "that", when "this" arises "that" arises, when "this" ceases "that" ceases. Not "this" in "that" or "than" in "this".

When Māluṅkyā,putta, you are ‘not by that,’ then you will ‘not be therein’.

When, Māluṅkyā,putta, you are ‘not therein,’ then you will ‘be neither here nor beyond nor in between the two’.

(Arahatta) Maluṅkyā,putta Sutta

There are many levels of absorptions which are described in the Suttas numbered from the 1st to the 9th Jhana:

1. Paṭhama Jhāna Pañha Sutta
2. Dutiya Jhāna Pañha Sutta
3. Tatiya Jhāna Pañha Sutta
4. Catuttha Jhāna Pañha Sutta
5. Ākāsânañc’āyatana Pañha Sutta
6. Viññāṇāñc’āyatana Pañha Sutta
7. Ākiñcaññ’āyatana Pañha Sutta
8. N’eva,saññā,nâsaññ’āyatana Pañha Sutta
9. Animitta Ceto,samādhi Pañha Sutta

In the 1st 4 Jhana you develop the following factors:

1. Movement of the mind onto the object (vitakka)
2. Retention of the mind on the object (vicāra)
3. Joy (pīti)
4. Happiness (sukha)
5. Equanimity (upekkhā)
6. One-pointedness (ekaggatā)

As you progress you have to drop the factors which you initially cultivated until only the last remain. This can be in order or out of order. Saṅkhitta Dhamma Sutta

The nature of the experience is also given in Sāmanna,phala Sutta:

He permeates and pervades, floods and fills this very body with the zest and joy born of solitude.

...

.

meditation as distinct from (even deliberately renouncing) any other activities

It is born out of solitude. More on this see: Viveka,nissita by Piya Tan

One way to progress in the path is "a mind seized by restlessness". (Yuga,naddha) Paṭipadā Sutta Kōan seems to be doing the same. (How do kōans work?) But thi is not the pured form of concentration as there might be Vipallasa, Verbal and Mental Fabrication, Mental Nutriments (Ahara) and unwholesome roots.

Once many many years back I read Robert M. Pirsig's book, “Zen and the Art of Motorcycle Maintenance (ZatAoMM)” . It was a powerful book. Still to this day I recall that experience of reading it. It was Pirsig who once said, “The Buddha resides as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain.” Little incidents that I recall from this book are moments of “Samadhi”. So what is “Samadhi”? It is nothing but a mind established, a mind solid in its footing. Thoughts may come to mind and thoughts may go, but without destroying the concentration. When you are riding, surrounded by the passing scenery, and no obstacles in-between, you are in the midst of a spaciousness where thoughts can come to mind but without destroying the concentration. Thoughts would come and go, but you are in oneness with that moment of time in Samadhi. You are very much alive at such moments with the mind in the right center for itself in the body. Everything feels just right. It is a moment when the mind settles down in a healthy, sound, and wholesome way. Sadly in wearing a protective helmet you will not experience this oneness.

Such moments can happen even when you are in the middle of some activity, in this case when riding a motorcycle. It may not qualify as jhana, even though some people tend to equate Samadhi to Dhyna which is a meditative stage. But it’s a steady foundation. It’s a foundation of mindfulness. It’s an establishing of mindfulness. In this book, ZatAoMM, the narrator brings about Rumi’s ‘Rubàiyat of Omar Khayyàm’ as a nimitta for the Samadhi state. He would recite the Rubàiyat of Omar Khayyàm, to himself as he rides along. Rumi happened to come to deep Samadhi states in his grief over the untimely death of his mistic friend Shams. In his grief Rumi would go round and round a pole in his backyard and reciting poetry off the top of his head – what came to be known as the Rubàiyat of Omar Khayyàm.- that were full of deep spiritual wisdom.

It is not entirely incorrect to define creative acts as those that are divinely inspired – inspired by the ‘God within you’. Great works of art are created when the creator is in a state of Samadhi, when such qualitative works are done. Setbacks at such times are gumption traps as the narrator describes it in ZatAoMM. This state of Samadhi (or the quality that the narrator seeks in ZatAoMM) is a state of sacredness can not be precisely defined because of its subjective nature. It is an unseen force that nourishes and illuminates, but ultimately transcends the physical world. As the Tao te Ching says, the way of the sacred “is like a well: used but never used up. It is like the eternal void: filled with infinite possibilities. It is hidden but always present.”

Specially in Japanese space and spatial concepts, we can see this manifestation of the sacred. In the search for the manifestation of the sacredness we could look at the Japanese ‘tea ceremony’ as in this enclosed space we can find the true spirit of Japanese space. This is another of the many creations of an artist, creating a space of Samadhi according to Zen. In his book, “The Zen of Seeing,” (1973) Frederick Franck explained about this intuitive self that helps make such creations:

“Who is man, the artist? He is the unspoiled core of every man, before he is choked by schooling, training, and conditioning until the artist-within shrivels up and is forgotten. Even in the artist who is professionally trained to be consciously ‘creative’ this unspoiled core shrivels up in the rush toward a ‘personal style,’ in the heat of competition to be ‘in’…. I believe that in seeing/drawing there is a way of awakening the ‘Third Eye,’ of focusing the attention until it turns into contemplation, and from there to the inexpressible fullness, where the split between the seer and what is seen is obliterated. Eye, heart, hand become one with what is seen and drawn. Things are seen as they are – in their ‘isness.’ Seeing things thus, I know who I am. [Franck. p.15] ”

In this book on learning the art of sketching, Franck tells us how to get in touch with this collective unconscious – our intuition – and how to be in oneness with ones subject in a state of Samadhi. The Tea Ceremony, and it’s environs, are an example of architecture that fosters this quality of Samadhi. I would say that such places are spiritual. These places help one to dwell in the eternal timeless present and live the truth that one understands, immediately. Truth is never in the past. Truth is a living thing, and not within the field of time. Sacredness is not found in the past, in memory. For the Japanese, space is experiential and sensuous unlike that of the west, where space is more objectively conditioned by shape and measurement. The Japanese tea ceremony, which has had a far-reaching influence on all forms of art, is a good example of this experiential approach to space.

It was the Japanese tea master Sen no Rikyu who further improved the tea ceremony, though it existed long before as a way of entertaining the visitors who come to a Zen Monastery. He created a distinct space that was later accepted throughout Japan, called wabi-sukiya space – a designated space separated from the outside world, for the purpose of drinking tea. Originally a pastime of the upper classes, this was widely adapted by the common people by the sixteenth century. The tea ceremony (Cha-no-yu) brings together four spiritual elements: harmony, wa; reverence, kei; purity, sei; and tranquillity, jaku. These four elements join in making this ceremony a success. All participants of the tea ceremony must be in harmony with each other. In the days of the samurai, to participate in the tea ceremony, the samurai had to remove the sword that symbolised his social rank. Within the room all are considered the same irrespective of their cast, creed, race or religion. The participants would talk with reverence to each other on subjects of mutual interest. The tea ceremony incorporated in it the aesthetic appreciation of poverty that emerged by the end of the medieval period. Rikyu’s art of tea is called wabi sabi, meaning poverty of simplicity. In Buddhism the word sabi is understood as a state of absolute nothingness, a state of void, that is every Buddhist’s ideal. The simplicity of the teahouse, sukiya, is derived from the ceremony of purification where the participants strip themselves of all but the simplest and most basic characteristics. Suki-ya, which literary means gap-space, was used for the teahouse as it is separated from the main dwelling. This implies that suki-ya/teahouse has been derived by the concepts of void-space, that Lao-Tzu considered as dynamic. Thus, Taoist emptiness and Buddhist impermanence dictated the distinct spatial idea of the teahouse.

The teahouse, both within it, and without, characterises the impermanence of all things, that life is an ever-changing phenomenon. The teahouse consists of a tea-room that can accommodate a maximum of five persons, an anteroom or mizuya, where the tea utensils are washed and kept ready to be brought in, a waiting room or machiai, where one has to wait till the ceremony begins, and the garden, roji, which connects the tea-room and the waiting room. The waiting room protects the visitor from the weather while reminding the person of the ever-changing nature. Two other elements that imply impermanence are the primitive lavatory near the teahouse, and the gate. The simple privy symbolises the incessant changes that process the human body. The gate to the teahouse signifies the constant passing in and out of visitors. The roji, garden, helps break the connection with the outside world, and is in itself the first stage of meditation. Generally the garden is planned in the kaishyu or stroll style.

'Samadhi' generically means 'collectedness' or 'concentration'.

The Pali states there are two types of concentration, namely, 'right' & 'wrong':

In one of right concentration, wrong concentration is abolished...

MN 117

'Right concentration' is defined as concentration that has seven supporting & requisite factors:

Any singleness of mind equipped with these seven factors — right view, right resolve, right speech, right action, right livelihood, right effort & right mindfulness — is called noble right concentration with its supports & requisite conditions.

MN 117

Therefore, an expert marksmen trained to assassinate people in war has 'samadhi' but it is 'wrong samadhi' because it is not supported by the above seven factors.

In fact, if a 'Zen samadhi' is not supported by the above seven factors, particularly 'right view', it is not 'right concentration' according to the Pali.

As for the word 'jhana' or 'absorption', this generally refers to a 'meditative' concentration.