Pure antimus beings from the antimus side of the multiverse are unaffected.
It’s the hybrid animus-antimus creatures bound together with Necromancy or infection (which was possibly created with necromancy) that’s affected. It’s the magical bindings that are designed to tie antimus and animus together that get screwed up because suddenly there is no more polarization.
So it’s the bindings that hold the antimus in the animus created bodies is what causes the problems.
This is why ghouls are unaffected. They are alive and have an antimus infection, they go to the Abyss, the infection is neutralized (at least while they are there–not clear what happens when they come back–although we will soon find out)
Vampires? Not clear what happens with them, but they’ll probably be sick. Liches will be severe distress as will zombies and other animated undead.