Vader and snoke could be the same people but then again maybe not, we've heard rumours snoke is a new character but how many spoilers have we all seen? Vader could've have been pulled out of the ashes like what had happened before he got his scars.
How do we know that snoke isn't a sith lord, how is he a supreme leader if he isn't a lord of the sith? Why does ren pledge his allegiance to snoke so tight, like the way he talks to his grandfathers helmet?
I for one believe that snoke could and may well be lord Vader, but then I may be wrong in so many ways.
We may have to wait and see what will happen in the next movie and maybe they will give us a little bit more story before everything happened before the genocide happened, because we still don't really understand what has happened before all this.