Are these Bible verses referencing UFOs?

It can be, or it could be something entirely different. It is for us and the future generations to understand the signs when they occur, and take a stand. John's narrative (at that point of history) is like a child or perhaps a lost Amazon tribe deep in the Amazon forest that sees a jet flying overhead for the first time. Most probably the child/tribe would describe it as a "huge bird (assuming the child/tribe already knows about birds) with a roar like a lion (assuming it knows about lions) and with a flaming tail of fire that buries everything behind it in a smoke".

Even a hundred years ago at least some people would have shaken their heads in disbelief or laughed at the words "a stone fell on earth and destroyed a part of it", or "a star fell from its perch". But today we know that a one mile stone (meteor) is enough to blow away a small country, and dying stars do seem to fall and fade at once when observed from earth.

Going forward more of the Revelation would hopefully become clearer. For example, scientists are now theorizing about the possibilities of invisible gateways/fields that open between galaxies, and traveling through them, and black holes etc. So perhaps the "channel that opens in the sky", or the "bottomless pit" may become clearer in the not too distant future.

Here is one of the most remarkable descriptive passages in scripture. If you believe in flying saucers, then you may think Ezekiel is describing one here. However, the other elements in the narrative rule out the idea of a flying saucer controlled by aliens from another planet.

Cherubim and a Throne In this portion, Ezekiel sees four four-faced cheribim standing beside a house. Above the cheribim was a throne, and a voice from the throne commands a man by the house to get coals of fire:

Then I looked, and, behold, in the firmament that was above the head of the cherubims there appeared over them as it were a sapphire stone, as the appearance of the likeness of a throne. And he spake unto the man clothed with linen, and said, Go in between the wheels, even under the cherub, and fill thine hand with coals of fire from between the cherubims, and scatter them over the city. And he went in in my sight. Now the cherubims stood on the right side of the house, when the man went in; and the cloud filled the inner court (Ezekiel 10:1-3).

Cheribim and Wheels Here, we learn more about the wheels and their relationship with the cheribim. Some ufologists claim that these wheels are windows around a flying saucer. You be the judge:

And it came to pass, that when he [God] had commanded the man clothed with linen, saying, Take fire from between the wheels, from between the cherubims; then he went in, and stood beside the wheels. And one cherub stretched forth his hand from between the cherubims unto the fire that was between the cherubims, and took thereof, and put it into the hands of him that was clothed with linen: who took it, and went out. And there appeared in the cherubims the form of a man’s hand under their wings. And when I looked, behold the four wheels by the cherubims, one wheel by one cherub, and another wheel by another cherub: and the appearance of the wheels was as the colour of a beryl stone. And as for their appearances, they four had one likeness, as if a wheel had been in the midst of a wheel. When they went, they went upon their four sides; they turned not as they went, but to the place whither the head looked they followed it; they turned not as they went. And their whole body, and their backs, and their hands, and their wings, and the wheels, were full of eyes round about, even the wheels that they four had (Ezekiel 10:6-12).

Literal Wheels When Ezekiel described eyes and wheels, was he trying to describe something otherworldly in his own limited language? This following passage says otherwise. We learn here that “wheels” is not Ezekiel’s best attempt to describe something, but a word he heard spoken: “As for the wheels, it was cried unto them in my hearing, ‘O wheel’” (Ezekiel 10:13).

Two main things are happening in this chapter. God’s presence was leaving the temple, which was in Jerusalem, and he was about to pour out judgment (the fire taken by the man). Jerusalem was later set on fire.

I’ve never heard of an account of a UFO that included four-faced, winged creatures and a throne set above it all. So it is difficult to square this passage with flying-saucer UFO accounts.

Depends on how UFO is being defined. Extra-terrestrial? God and his angels are also extra-terrestrial! But, I assume you are meaning life outside of Earth, but not including heavenly beings. In which case, then, these cases you mentioned aren't "UFO's"

In the first example, the things being referred to can be seen in verse one:

Now it came to pass in the thirtieth year, in the fourth [month], in the fifth [day] of the month, as I [was] among the captives by the river of Chebar, [that] the heavens were opened, and I saw visions of God.

This where the wheels came from. It can be clearly seen that, the wheels, came from Heaven. Being so, it would have been a heavenly object, thus, disqualifying it from being a UFO.

The second example given, was actually the angel of the Lord, not any extra-terrestrial object, thus, not a UFO either.

A whirlwind is obviously not an extra-dimensional vehicle, as whirlwinds appear everyday.

What might pass of as an extra-dimensional vehicle, could be the "chariots of fire, and the horses of fire" that took Elijah up into heaven:

1 And it came to pass, as they still went on, and talked, that, behold, [there appeared] a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven.

However, it could be argued that, as these are coming from Heaven, these are still heavenly beings or objects, and thus, not UFOs