Are you talking about moving the unit out and demo'ing the washer/dryer connections in the guest bathroom? Or are you going to leave the connections in place and just move it outside because that is where you want it? If you are leaving the connections in place, go for it. All the realtor would have do is say that there are two washer/dryer hookups and show them the area in the guest bathroom.
If you are going to be removing the connections, I would not do it. The best part about my house is being able to do the laundry whenever without having to worry about the weather or dragging laundry baskets out of the house.
As long as you leave the connections in the house, actually having a washer/dryer unit hooked up will not hurt the sale of the house, unless someone is trying to find a house where they can bundle those into the sale of the home.