Interesting idea. Most King Crab Legs you buy are pre-cooked and frozen so it would be a matter of heating them up and not over cooking them. I suppose you could heat them up in the smoker at a high temp 350-400 degrees for 10-12 minutes? With the short time in there I'm not sure if it would take enough smoke to flavor the meat. I'm not sure if it is safe to heat them up low and slow
Maybe someone else will have more knowledge about this.