A problem you might run into, depending on the campground is when your friend arrives. Will they have to go through a gate with an attendant? That could cause issues. And if staff sees someone leaving and another person taking the site, that might raise a brow. I would just call the campground and let them know what is going on. It's the right thing to do. The park deserves the right to know who is staying in their park. If by chance your friend has an issue or some trouble is caused, they might be looking at you as the registered camper.
