One of the neat things about Snoova is he bucks the 'goody-two-shoes' Wookiee image. In fact, other wookiees don't even like him. Details are sketchy, but in the past he apparently used his claws in unarmed combat, which is a seriously big no-no. This got him labelled 'Madclaw' by other Wookiees, and he either got banished from Kashyyyk or got a Death mark placed on him because of this. I have read it both ways, which seems redundant. If you want him dead, you don't exile him, then put him on the hitlist. You throw him in jail and just kill him.
No, What I think happened is this; he used his claws and got Banished. Then he went out and became an infamous bounty hunter, bringing further negative attention to Wookiees. If they ever set a death mark on him, I think this might be the order in which it transpired. I'm no expert or Canon authority, but that makes more sense to me.
Besides, claws are pretty crummy weapons when compared to Snoova's Vibro-Axe, which he is seen with in the photo above, which comes from the Star Wars Galaxies Trading Card Game - Galactic Hunters.