When you do deadlifts, your shrugs aren't working through a full range of motion but they're still being worked a lot because they have to contract to act as stabilizing muscles. If you wanted to do shrugs, I'd go ahead and just throw in some shrugs after deadlifts like you would biceps after back, or triceps after shoulders. I wouldn't do very many sets of shrugs, maybe 2-4 total sets for traps.