I wouldn't be too confident about something when it comes to Warhammer... It's not like it's unheard of that Tau lost a battle.
Right, as our daemonic masters would have already reached your lines and be ripping you apart one by one, filling the air with your screams. We'd have no time to reach you before your heads were on pikes, and skull claimed by the daemonic barbarians of Khorne.
Well if Tau and Chaos form an alliance,lets allow the tryands to be part of the Adeptus Custodes ,shall we?
Different level entirely, Chaos forms a temporary alliance/manipulates Orks. There is little difference here except that the Tau are disgusted/terrified of Chaos.
huge difference but i get your point more of the difference between the IG death kreig and Eldar teaming up
Fluff wise Commander Farsight is aware of the beings of chaos I won't go into detail as it will be a spoiler but Farsight felt something manipulated events to occur for him to notice this unnatural influence the Ethereals had on the rest of Tau. Also why would a race that preaches Unity even think of allying with rebels? Just wouldn't make sense at all.
easy answer to that last bit the tau care little for who it is they want to unify every race trust me tau and chaos isn't as bad the Tau tried allying with necrons 1nce