Is the chaffee up-tiered?

CatStalker: I have seen a chaffee in a tier 5 battle, but what is actually happening there is that it's a tier 7 game, but the chaffee is the only tier 7 (even though it's a 5). The same thing happens during the rare time you see an arty such as a hummel at the top of the team in what looks like a tier 5 game.