EDIT: So I think I might have found a workaround using the biome condition. Adding a biome condition to the skill makes them remove themselves, but gives that annoying flash since it takes a few ticks for them to remove themselves. Adding a biome requirement to the random spawners seems better, even though you gotta take some time to set every biome you'd want the mobs to spawn in. I checked to see if there was a notinbiome condition but didn't see one in the manual, would be useful...
NotInRegion Condition
NotInRegion Condition