I was thinking that the Sentinel was an old Imperial piece, and like the troops, is in the service the Tau. It would essentially BE an Imperial Guard unit, pilot and all, like the human auxillaries, but perhaps upgraded by the Tau (as Kroot shapers can be given a pulse rifle). True, the two armies are similar, but I think that's why it'd be easy to throw in a squad of human auxillaries, just to add some depth to the army, not so much firepower or tactics. Also, I need something to break up the color scheme. Also, I think I'm gonna add some capes to my Pathfinder team and give them a camo scheme, make them look more like a scout team then I currently have them. Top link is for the human auxillaries, bottom is what the cape would look like.
http://us.games-workshop.com/games/40k/tau/painting/guela_aux/default.htm
http://us.games-workshop.com/games/40k/tau/painting/bandpconversions/default.htm