The idea that the shinigami is the Uzumaki ancestor is interesting , that was the idea that made me think that Hamura was the RDS.
We saw that Hamura had byakugans , no points above his eyes , not the same horns , no similarity with the shinigami.
It seems like Hamura is not the shinigami and he , or his daughter , seems to be the ancestor of the Hyuuga clan.
If the Uzumaki ancestor is also Hamura's daughter , what kind of relation is the Naruto/Hinata relation?
Hagoromo's red hair and Hamura's Byakugans killed my hope to find a hypothesis where Hyuuga and Uzumaki were not related by blood at some point.