Blight also provide 2 HP regeneration per second for undead units, at any time.
So it might be a good idea to bring some sacrificial skulls along just to add to the already massive healing undead has (unholy aura lvl 3 = 1.5, statues = 12, blight = 2, total 15.5, equivalent of a healing ward healing grunts).
I don't do it myself though (bringing sac skulls in battle).
Also interesting to note that trees that the ghoul touches becomes dead.
