I'm blind and a guide dog handler. Most of us clean up after our dogs just like any other dog owner (as in any group of people, some are more responsible than others.). It takes a little different technique to clean up than a sighted owner would use, but it's not difficult and seldom is any assistance required.
Good question. I think the dogs and their owner are taught that the dog should empty itself in a particular place before it starts its work. Then the owner or a helper can clear it up.