I'm not really seeing the 'why would I use undead when divine enemy in game' argument, there is literally no mention anywhere of anyone having an ability with greater effect against undead. Willy's character has magic divine in origin, but that doesn't mean anything, Hades is a 'divine' in that same respect, do you think his powers would be somehow super-effective against undead considering his sphere of influence? The only slight mention of being super effective against undead is an ability which has elements of the sun, making it super effective against 'certain enemies' presumably people with a weakness to the sun, such as Vampires.

I'm not seeing any particular 'hard counter' here, certainly not in the same level as 'uber water shield'.