Capturing a Galaxy: An exclusive interview with @AnnieLeibovitz discusses her #TheForceAwakens @VanityFair photos. http://t.co/umCbvWHJOI— Star Wars (@starwars) May 28, 2015
The Vanity Fair article says this about the character:
"A previously unpublished photo of Andy Serkis, also sporting mo-cap gear for his portrayal of Supreme Leader Snoke, is available here exclusively."
So, now we know who Serkis is playing and that he will in fact be in mo-cap gear for this role.