How about Roshi? OMG Maximum Funniness Potential to see Controller Roshi.... and the ability to sense KI, DOUBLE ki in a lifeform (an infested host), would be SUPREMELY useful.
I've thought about writing a fic where the Animorphs acquire Gohan, who has come to the DBZ universe. SUPER SAIYAN ANIMORPHS, now THAT'S epic awesomeness... plus they could EASILY find out who Controllers are, start liberating them, but would Rachel have an easy time controlling the Saiyan instincts... or not?