Given what happened during the historical plague, it's safe to say that everyone will be blaming everyone else. Allowing one race to have a heightened immunity creates the question of why they wouldn't take the opportunity to strike out at the devastated nations around them.

Plus, I think to have the dwarfs hit just as hard as the other intelligent peoples creates adventure opportunities for classic dungeon crawls, as abandoned dwarf outposts and cities will be quickly occupied by goblinoid hordes or orcs, plus whatever creeps up from the Underdark.