&^$&#%#^#$&! I had a whole list of enemies unetheric Voice of Wrath failed to work against and some it worked against, and then I misclick, list gone. :(
So here, mostly from short-term memory:
Fail: midgard security, fang ganger, heli drone, spider drone, midgard scientists (sane and insane version in damaged buildings), writhing mass, officer Stone, twisted hound, hound drone, fang gang enforcer, third eye poser, roaring drunk, bat swarm, drunken challenger, punk student, and a pvp opponent who was probably/possibly not etheric.
Green flame surprise: 3rd eye sorcerer, 3rd eye ganger, insane slasher, third eye hunter.
I think the target has to be tripping the ether in order to activate the green flames without being etheric yourself. And apparently, most enemies are not etheric.