I remember years ago when I found these weird Centaur-looking lizard things holding bio-mechanical weaponry on clearance at my Local Games Shop (LGS). At the time I thought they would make great antagonists or underworld creature for my Necromunda game, so I scooped them up for a steal. It was only recently that I brushed the dust off of my Zoats, a little curious how they fit into the 40K universe. The 40K wiki provided me with some enlightenment:
"The Zoats were introduced in the first release of the 40K game Rogue Trader. They are described as one of the Tyranid's genetically engineered slave races, in the first White Dwarf army list for the tyranids. They were discontinued by Games Workshop in the second edition of Warhammer 40,000, and have since disappeared completely from the mainstream. They were elite fighters, forming the warrior-corps of the Hive Fleets. Although naturally a psychic race, they could not develop psychically under Tyranid dominance. It is stated that the "Xenobiologers of the Administratum" believed Zoats to have been created purely for combat. In game terms, any Tyranid force had to have at least half its numbers made up by Zoats.
The Zoat's exact links to the Tyranid race are lost outside of the Warhammer 40,000 galaxy, but what has been gleaned from ancient encounters is that the Tyranids did not assimilate the Zoats as per the norm, but instead enslaved them to do their bidding. They were large, strange, powerful creatures, centauroid in appearance, with two powerful arms, and a lack of oral organs. The Zoats communicated telepathically, and had a prodigious ability to assimilate the cultures (language, customs, practices) of other races, thus acting as diplomatic conduits for the otherwise uncompromising hive mind. 
In this role, they were said to excel, but were discontinued from use by the Tyranid race once the Zoats rebelled against their pitiless enslavers.
Though used for communicating with other races and other diplomatic tasks, the Zoats were proficient fighters, said to be savage, ruthless and ferocious in battle. Even so, all out war between a small sub-part and the rest of the Tyranid race could have only one outcome, and the majority of the Zoat race fled from the Hive fleets.
As such, they were one of the first Tyranic organisms to reach the Eastern Fringe, and have been the only Tyranic organisms so far to have actually established contact with the Imperium of Man.The Zoats were regarded with great curiosity by those they encountered, and were said to travel in fleets of "great, conch-like ships". However, their general nature and frequent contact with other alien races in the sector, as well as frequent attempts to settle on worlds caused the Imperium to declare them "Xenos Horibillis", sparking the violent Zorastra-Atilla war in the 38th millennium, which lasted fifty years, culminating in the destruction of the last of their strange colossal ships over the planet of Zorastra. As there were no subsequent records of contact with the Zoat, it is assumed that the Zoats have been purged from the galaxy.
In the recent Horus Heresy novel, Fulgrim, aboard the multi-racial (or more appropriately "multi-special", seeing as there are a number of species as well as humans) Diasporax fleet there could be found a number of crimson centaurid creatures. Although not named as such, there is a strong implication that they are Zoats."
The Zoat story just doesn’t jive with today’s Tyranids' and their treatment of the universe like some big "all you can eat" buffet in their uncompromising compulsion to consume all existing biomass. What I want to know is do the Zoats have a place in the current 40K universe? I think the Zoat race and their story would better fit in with the Tau Empire, since the Tau take in or hire just about anybody that want to fight or aid the "Tau'va", The Greater Good. On the table-top Zoats could represent a potentially strong or specialized psychic unit(s) and maybe, based on their earlier description Zoats could augment ally and/or enemy troop morale. There is a considerable focus on psychic warfare in fifth edition (5E), so perhaps this would actually benefit the Tau codex (seeing as how I have yet to read it).
What do you think?
In conclusion the Zoats went the way of the dinosaur, receiving a big eviction notice from the 40K universe. In good company, the Zoats joined the dwarves, chaos dwarves, and squats in the pink-slip hall of fame. Which is a little sad because I think Zoats are interesting characters, and have great potential. When you consider the fact that GW has a hard time updating current race codices to fit into continuity of 5E, however, asking for more armies seems unjustified. That is why I think it would be neat if Zoats became an addition to an existing army.