Stamina also boosts the HP growth at levelup, but not enough to make it worth boosting it. Also, word is that the Vigor stat doesn't really work.

And yes, undead monsters are completely healed when auto-dispatched.

While we're at it, you should know that the "evade %" stat doesn't work. A bug in the game makes physical evasion based on your magical evasion (mdef % or mblock %, don't remember).