Not smart enough to realize that Tobi was Obito. But OK.minato knows pretty well that it requires a powerful person like madara to control the size of the nine tail demon fox. not all uchihas have the power of madara. if obito was able to control nine tail demon fox was because of the infused chakra of hashirama. Minato is smart enough to rule out the uchiha clan. Minato was recognized as a genius by the village. Not only third hokage would have been on his side but also many others. danzou wouldn't have been able to say anything had minato survived