I still don't understand... why take it just because it's incredibly cool and rare?
What's the point of taking Leadership if it doesn't give Battle Discipline? But if it does happen to appear, then Diplomacy, Messenger, and Money are good choices.
And Light would also be good if there are spells. It has Righteous Strike and Stone Skin... and more.
So, Empathy doesn't work on them because they don't have morale, so the hero won't be affected, and Money, Diplomacy, and Messenger aren't worth sacrificing a skill for.
But Light magic will still be a good enhancement for Necromancers after Darkness, and not just after Darkness.