No lol you can sleep mobs anywhere in the dungeon ( doesn't need a lock out boss barrier )
Once they r asleep just run a certain distance away from them and it'll cause their aggro leash to break.
Similar to the big hecta guy in Copperbell Hm ( the 1st after u go down the 1st elevator at the entrance ), if u run right past him he'll drop aggro for some reason and just continue patrolling.