Not Necessarily, no.
Not all Undead are that level of affected by Positive Energy.
We are also talking about Ritual levels of undead I can imagine, which complicates matters, not to add to the fact that we are talking about a minion of a being who has had thousand years to collect energy, and also invented Necromancy. My research led me to believe that Necrophtius could create undead without tiring for longer than any of us could live. Lets add to that that his Arcane Sons, have been collecting lots of energy for a purpose we don't know.
I would imagine that any average undead, my for instance, my die, but definitely nothing on the level of threatening that we are dealing with here.
-Leliana Kainen
OOG:Chris R.
Storyteller / Marshal