I find that unlikely.. Tau don't let most Tau join their government. Their government is, essentially, a group of pheremone secreting God-kings whom noone can question.Tau are willing to peacefully induct humans into their government...
It's not uncommon for Tau. They don't go in for random massacre very much, so what happens when they capture territory and you're left with a bunch of uncivilized barbarians occupying it?And I suppose sometimes Tau would force a POW situation (uncommon as that is in the 40k universe hmm?)
And yet this is a pretty singular example, and it was only implemented because they rebelled against Tau rule, and in the end they still got a hell of a lot better treatment than people who resist IMPERIAL rule get. Generally the Tau like to win through cultural means and not force of arms, only resulting to fighting when need be.The tau are the biggest @$$holes in the Universe.
Everyone else admits to hating everyone and kills them to their face, except maybe Eldar as they are sneaky gits.
But the Tau? Oh no, they'll 'liberate' your planet and set up reeducation facilities to teach you the ways of the Greater Good.
In DOW Dark Crusade, the Tau ending basically says that they didn't kill the Human Citizens, but they did put them in single sex reeducation facilities for years.
As a result the humans couldn't breed so they just died off leaving the world a Tau colony world.