You don't need IVU to enter the room. Just invis up, run through the Beastlings room, open the door and hug the right wall. The Haunts all spawn in the center and left side of the room. The right side is safe.
It's a big room. Plenty of room to fight comfortably.
The respawn time on the Haunts is 18 minutes.
The only items that seem to forage in the room are Water Flasks, and Mushrooms.
I sat through 4 spawns of the haunts, and Dreameater never popped. I'll come back later...
Dru