I'm with Leroy/Cane; it is Kabuto. Consider Kabuto doesn't have a chakra signature because he doesn't have an identity. Karin wouldn't possibly be able to sense his true form. But I do like the idea of the Sage coming back somehow... It'll happen eventually. Isn't it ironic how those items land on the only Ninja good at using The Sages items (Tenten). That's the only part of the chapter I did not like. That was pure silliness.