No, I don't think GM is the real Body of the Jyuubi, I'd like to believe that the real body is up there merged with the Moon, and that the GM is a Fake Body created by RS using Izanagi, to contain the Chakra of the Juubi and to divide it up. The RS is said to have sent the Juubi's body up into space in order to prevent it from being brought back. Perhaps he foresaw someone like Madara attempting to revive the Juubi.
In order to become the Jinchuuriki of the Juubi, Madara will have to acquire the Body of the Juubi. That should prove interesting if I am correct that the GM is not the body of the JUUBI.