>>532289073
Any of the abhumans, like beastmen, are an easy sell.
Between an Inquisitor, a Rogue Trader, and the questionable act that some system governors allow sanctioned xenos, they could squeeze in most anything
Votann mercenaries (space dwarfs)
Eldar (space elves)
Ork Mercenaries/Freebootas (though no one in setting would be happy about it)
Kroot Mercenaries
etc.