Yes, the International Ombudsman Institute, the IOI, states very clearly in its constitution--again, available on the Internet--how to qualify as an ombudsman, and there are different categories of memberships. The IOI carefully reviews ombudsmen's offices around the world to decide which ones qualify as ombudsmen and which ones don't qualify, and which ones have mid-status.
So the IOI would be the body that decides on proper accreditation for ombudsmen worldwide.