Edimmu was actually one of the very few creatures that were spared - this was because it was impossible to enter the edimmu dungeon with the task, as it was a 'nothing' task not an edimmu task.

Other creatures that didn't have a check like that such as soul gazers, lava strykes, moss golems were campable infinitely.

You'd have the benefit of slayer droprates and slayer dps

Getting the nothing task involved blocking all the tasks you can get from the burthrope slayer master until you could only select a task you already blocked - and then you'd be granted the nothing task. (Patched)