Oh boy.... *sighs heavily* First off it's Senju not Senji. Secondly the Uzumaki seem to pre date both Uchiha and Senju (though it has yet to be revealed in the manga it will be mark my words). I believe the Rikudou Sennin was half Hyuuga and half Uzumaki thus giving him the ability to see chakra and to have a body capable of sustaining the strain of being the Juubi's jinchuriki. Again this has yet to be confirmed and is my own theory but it is picking up steam as we get ever closer to the end of the manga. I find it interesting that Kishi has yet to reveal much about the Uzumaki's heritage yet their legacies (such as Shiki Fuujin, Bijuu compatibility, and overwhelmingly powerful life forces being the only Jichuriki's to have their Bijuu extracted and yet survive) are splattered all over the place; not to mention the main character is half Uzumaki and thus they must play a huge role in the history otherwise why make the main character an Uzumaki and not a Senju?
Nagato was able to utilize the Rin'negan not only to use the six paths but to also master all five elemental chakra natures, not even Madara (who claims to have awoken the Rin'negan) has shown that kind of power. This I think is a major clue that shows the lie in Madara's claim, but we shall see....
