Spirit armor and Ice/frozen armor protect you from any damage attack. (A damage attack spell has the closed fist icon) Some death spells that steal life, such as Ghoul, Vampire and Wraith are not concidered "damage" spells; they belong to a distinct different spell class (called steal life I think) that has a broken heart icon.
In short, armor will protect you from most anything except death life drain spells. This is by design.
