Is adultery grounds for excommunication or other discipline in a Jehovah's Witness Church?

Unrepentant, blatant and on-going adultery, whether resulting in a pregnancy and/or the break-up of the marriage or not, is condemned by Jehovah’s Witnesses and would almost certainly result in the guilty party being disfellowshipped, or expelled. Here are some extracts from their web site:

Some of the offenses that could merit disfellowshipping from the Christian congregation are fornication, adultery, h*m*sexuality, greed, extortion, thievery, lying, drunkenness, reviling, spiritism, murder, idolatry, apostasy, and the causing of divisions in the congregation... In the Christian congregation, the principle enunciated in the Law applies, namely, that two or three witnesses must establish evidence against the accused one. (1Ti 5:19) Those who have been convicted of a practice of sin are reproved Scripturally before the “onlookers,” for example, those who testified concerning the sinful conduct, so that they too may all have a healthy fear of such sin. Those who have been expelled may be received back into the congregation if they manifest sincere repentance. https://wol.jw.org/en/wol/d/r1/lp-e/1200001462

When elders serve on a judicial committee, their role is spiritual, or religious. Guided by the Scriptures, they judge whether the abuser is repentant or not. If he is unrepentant, he is expelled, and an announcement is made to the congregation. (1 Cor. 5:11-13) If he is repentant, he may remain in the congregation. However, the elders will inform him that he may never qualify to receive any congregation privileges or to serve in any position of responsibility in the congregation. Out of concern for the welfare of children, the elders may privately warn the parents of minors in the congregation of the need to monitor their children’s interactions with the individual. When taking such measures, the elders are careful to maintain the privacy of those hurt by the sin. https://wol.jw.org/en/wol/d/r1/lp-e/2019405?q=unrepentant+sin&p=par

Likewise, a servant of Jehovah today will be disfellowshipped only if he is unrepentant or continues to practice what is bad. (Acts 3:19; 26:20) If genuine repentance is not manifest to the elders who serve on a judicial committee, they must disfellowship the person. https://wol.jw.org/en/wol/d/r1/lp-e/2015287?q=unrepentant+sin&p=par

In most cases it is the unrepentant who insist on ‘practicing sin’ that are expelled, disfellowshiped from God’s organization. https://wol.jw.org/en/wol/d/r1/lp-e/1967125?q=unrepentant+sin&p=par

As far as adultery goes, Jehovah’s Witnesses do not have any “defined policy or set of guidelines, similar to the Catholic guidelines” as described in your link. All that is needed to know about adultery is to be found in the Bible. Adultery is condemned, but Jehovah’s Witnesses do not concern themselves with issues of “restitution to the offended party”. The guilty party (if unrepentant) has sinned against God and will answer to God. If unrepentant, they will be expelled from the congregation. I did not see any mention of that in the link you provided.

A simple answer to a simple question:

Is adultery grounds for excommunication or other discipline ...? ... I'm talking about openly unashamed sinful behaviour.

The answer is "Yes".

...and its called "disfellowshiping" instead of "excommunication".

Slightly extended...

By comments under your question and the obvious fact that this is a personal situation of yours that prompts you to ask, there are many circumstances which people run from that sort of discipline, and do seem to evade it. There are many circumstances where contending parties have different accusations and versions of a story. Obviously there is no divine revelation to reveal the true nature of what happened, so there is the obvious human limitations that keep things from getting solved.

With that in mind, many people successfully (seem to) evade discipline, but there is the simple fact that its not humans they are disobeying, or running from. Here is the more important thing:

Galatians 6:7 [Amplified Bible]:

7 Do not be deceived and deluded and misled; God will not allow Himself to be sneered at (scorned, disdained, or mocked [a]by mere pretensions or professions, or by His precepts being set aside.) [He inevitably deludes himself who attempts to delude God.] For whatever a man sows, that and [b]that only is what he will reap.

Compare to Proverbs 6:27-29:

28 Can one go upon hot coals and his feet not be burned?

29 So he who cohabits with his neighbor’s wife [will be tortured with evil consequences and just retribution]; he who touches her shall not be innocent or go unpunished.

Marriage is God's arrangement, and typically judged by God himself. Disfellowshipping is the least of one's fears when they are blatant and unrepentant in their course.