The FTC doesn't require franchisors or business opportunity sellers to register with it or any other government agency. However, several states do have registration rules requiring franchise sellers to register. Some of these states laws are tougher than others, but most have adopted the FDD guidelines for their disclosure requirements.
It would be a mistake, however, to assume that simply because a franchise is registered with a state or provides some type of full disclosure document, you as a consumer are going to be protected from the possibility of failure or rip-off. The only thing that a state reviewing agency can do is ensure that the franchisor has responded and filed the necessary documents.