Just tried this
Threw is in a room filled with 8(?) Fomors, constantly repopped after dying almost immediately. They appeared to be unsleepable by repose/lullaby/sleepga and couldn't be breakga'd (could be too low m acc.) Someone also commented that some of the mobs disappeared eventually, we wiped so we could exit and bring a PLD.
PLD to super tank mobs highly recommended
edit: it appears repopped adds have random hate, maybe pld/rdm to pull them immediately with diaga or something
edit2: after ~10min of killing fomors, 3 corses spawned. started spawning more as time went by even if you don't engage (people dc'd on wave pop) and then a Dullahan spawned and completely shit on us