Sorcerers Apprentice
Hero
You cannot legally rule that a bear is unarmed, since that would violate the constitutional right to bear arms.OTOH, we could lean on "natural language" to rule that the bear is unarmed (we just established that he didn't have a weapon) and he's striking with his claws, therefore, by definition, he is making an unarmed strike. I think that's a valid interpretation, and it would allow the bear (or someone Wild Shaped into a bear) to use Martial Arts with the Claws attack.