Seems to me like Oda's throwing a lot of ambiguity and contradictions to Kuma's behavior so we're not sure what he's like yet. Which I think is pretty damn cool, actually. Not the kind of thing you see in a shonen fighting manga, or even in this one.
Still, though, I do think Bart's seeking SOME kind of redemption for his past ways... Or else he wouldn't be so loyal to the government in the first place. Maybe Oda'll make him a tragic character.