Are there any existing in/out-of-universe evidence that suggests whether Snoke is a Sith or not?
It seems that it is generally agreed he is not a Sith Lord from the Banite order of the Rule of Two, given that he is believed to be at least a thousand years old. But is it possible he is a Sith Lord not from Darth Bane's order?
The Jedi believed the Sith are extinct but they are mistaken. The Sith believed there are only two of them in existence, but that belief originated from Bane - I haven't seen anything that externally supports that belief. That opens the possibility that Snoke could be a fellow Sith Lord who survived the war, escaped the Jedi's notice, and wasn't aware of fellow Sith survivors - and as such he's not compelled to follow the Rule of Two.
In other words, even if Snoke is proven to not be a Banite Sith, he's not necessarily not a Sith from a more ancient era.
Putting aside the above speculations in my head, what in/out-of-universe resources are there that have touched on this topic: whether Snoke is associated with or a member of the Sith Order?