It kinda does, otherwise two heroes with the right stun time could permanently stun bosses, making them incredibly easy. Heroes with enough luck and attack speed can already do this with a bash and/or cleaver. Some stuns seem to work though, like blackhole. It's a tricky balance, as heroes with stuns could potentially be way too strong against the bosses, because they could just permastun them or something, making the bosses unable to attack.
Also for the most part, it seems only the ogres, brood, wraithking, and the pudges are stun resistant.