For us, not needing a tractor to unload is a huge advantage of the dump trailer - but we don't stack our hay in the barn, either. We stack outside and rarely have to restack hay unloaded from a dump trailer. If your bales are pushed together tight on the trailer, they should come off in a solid row and stay that way if the ground's level. Mine's very often not, and we end up having to push a bale back in line once in awhile, but having to have a tractor to unload would defeat one of the biggest advantages of the dump trailer for us.
On the other hand we hardly ever feed more than 1 or 2 bales in a pasture at a time, so feeding with a dump trailer is something we would rarely do. We feed almost everything with a hydraulic bale spike on a truck, or occasionally with a tractor.