The only possible way Snoke can be Vader and have it make any sense at all is if a legitimate explanation can be constructed, I will attempt said explanation. If it were possible for a life force to split into two halves, one light and one dark, then and only then can we argue Vaders return as Supreme Leader Snoke. Humor me, as the "Return of the Jedi" ends Vaders light side passes and ends his struggle within himself of light and dark. If we back peddle and assume Vaders body was saved and his dark side remained then it may be possible to revive the dark lord. We did not witness Vaders body destroyed only that he was left on the death start by Luke. I am only speculating and theorizing to rebutle the original post. I do love the new Star Wars and feel is the best follow up to the original since the original. The fact remains and always will there will never be another epic saga as monumental as the original Star Wars with a villan as charismatic as Darth Vader/voice of James Earl Jones. History was made and we can only hope to follow this saga with an accurate and respectful continuation.
I firmly believe we shouldn't medle with the past/original episodes and should continue the saga with sensible story lines. If Darth Vader were revived with original costume (slightly updated) and James Earl Jones voiced him it would be a crime... a horrible but amazing crime that every true fan wishes could be explained and made possible. Good luck Disney this is a tough one and you are treading on hollowed ground. This could turn out to be movie history or tragedy. I hope this rebutle makes sense and was enjoyable. These are my opinions and based solely on my observations.