Well I guess all this discussion about how much of a badass Harald is is kinda moot now. Also, do the ghosts killed during nightmares count for things killed? Because that's kinda silly.
This spell can be controversial because every time the target commander survives a Vengeance of the Dead, the number of souls that returns on a subsequent casting increases until the commander simply cannot kill all of the units before the 75 turn limit. After 75 turns, the commander automatically dies, making the spell a guaranteed kill if cast enough times over enough turns.