Some odd though struck me today after remembering a quote from Dawn of War, when the Tau encounter Chaos troops on the battlefield:
It then occured to me that I have never seen any fluff that describes an encounter between the Tau Empire and Chaos.*Gasp* Human Madmen!
Do the Tau understand the difference between the Imperium and the Traitor Legions? Do they understand the whole Chaos thing or do the Tau just see some humans as crazy men with bigger axes?