I seem to remember that the Tau is an "ally" of an Inquisitor, and the Inquisitor, who may or may not be allied with the Tau race, and this Tau, who may or may not be allied with the Tau race, are benefiting from the Inquisitor's "I'm an Inquisitor!" power to have him be on a Kill Team, serving his and/or the Inquisitor's wishes.
Sorry did I just wander into a Matt Ward fluff discussion?