1. Knew
2. Obito had his rinnegan on his senju part
3.that's derps not mine sir so respect my theory I made
Fair enough. But let's move unto this Juubi part.
We know that the Juubi was within Rikudou Sennin when he conceived his sons (whether through Banbutsu Sozo or mystery wife), due to how the Elder Son also received the Rinnegan. Otherwise, the Elder Son would have to acquire his younger brother's DNA to awaken it for sure (regardless of how close they are in lineage, these two boys are portrayed as two halves of one body).
Transitioning into this, it's logical to verify that, because the Juubi is the houser of Senju/Uchiha DNA (since it was within the Sage when he conceived his sons), the Sage did not have the Rinnegan when battling it. This makes sense, because the Juubi is the one that houses The One Great and Ultimate Eye (or whatever you want to call it). It's the progenitor of the world, and the progenitor of all dojutsu.
it's a example because the sage is a uzumaki and had seal and people say he gotten rinnegan from juubi then nagato should have had it to obtain rinnegan but his genes made him control the rinnegan
Remember that Nagato was a fantastic suitor for the Rinnegan, because Uzumaki shinobi/people/peeps/homieG's are relatives of the Senju clan, which is a key genetic ingredient to housing it. Obviously Rinnegan is an eye derived from Madara, thus already contains Uchiha DNA.