Techcnally they are curses, a disease doesn't bring you back from the dead, the infection you can contract from a vampire during a vampire attack is the disease which carries the curse with it.I hope that these polymorphs do not happen. I think it would cheapen the overall experience of being a vampire or werewolf.
Of course, I also think BOTH of those systems should get a really extensive overhaul at some point so they include the different strains of their diseases and so they are actually blights and not boons.