SO6p WAS An uzumaki..
First off, title, now some reasons why I believe this..
1. Uzumaki's Possess Strong Bodily forces
taking more pain then average human..
still could protect naruto after going through childbirth AND an extraction...
lived for at least 90+ years...
took Chidori Spear head on, which chidori normally is an insta kill on average shinobis..
2.So6p's Family was known for sealing, this is why so6p was so good at it
Now, how do you expect some HUMAN to seal the FULL Juubi... And for the people saying he had rinnegan before Juubi, no. Juubi + Uzumaki: Rinnegan but I will get to that in a second...
Edit: Uzumaki Wasn't formed at the time, after smart debates I realize this. But So6p was the first technical uzumaki, I'm guessing his family used fuinjutsu but they didn't know the secrets of it, he figured out the secrets..
An uzumaki with the Juubi's DNA can form rinnegan..
How does this work?
The So6p Split his BODY and his Eyes right.. he didn't have a spouse, he used Creation of All Things..
His eye powers originated from Juubi, Uchiha's are distant relatives to the Juubi as Senju to Uzumaki!
Where am I Getting at?
Senju + Uchiha: Rinnegan
Senju's are distantly related to Uzumaki as Uchiha for Juubi..
Comments, Questions? I'll take em. Just needed to say this..
Edit: The Theory Stays the same, but uzumaki hadn't been formed at the time, So6p figured out the secrets of ninjutsu and made fuinjutsu, his FAMILY that he was born into learned this and Formed the uzumaki clan
But everything else stays the same, he is a technical uzumaki