This isn't even a common occurrence, or something that is being abused, and there is no reason why a Necro WOULDN'T be able to order undead while ethereal. What, just because they can't touch him, he can't talk to them? BS.
As I said. Someone lost a fight, and now he's butt hurt. period; and yes, I would buff the hell out of some maledictions. Why would anyone be able to just "wait out" the Bubonic Plague? It only killed a third of a continent in it's hey day.
It isn't like massive armies of newb Necromancers are rolling through Morea on a daily basis, so quit crying, wash the tears away, and go do something about it. Since Ethereal is not a spell that Necromancers have, my guess would be he doesn't have an infinite ability to use it, so go get your ten Paladin friends, and spam BoG and SoF like you always do. As far as the guardians getting waxed, what really needs to happen is the CRS system which prompts people to attack cabal guardians to begin with needs to be done away with.
Don
*Still lacking any sympathy*
In a game like D&D if something is on the ethereal plane, you can't see or hear it.