They aren't in the movie(that we know of) and the sith we saw isn't one of them resurrected.
The rumor has been for months that the 'apprentice'/Vader character(Adam Driver) of the saga is this Sith Wannabe. Felt the dark side at a young age but with the Sith dead he had no one to teach him, so what does he do? He searches the galaxy for Sith artifacts, holocrons, lightsabers(the one he had in the trailer could be one of these artifacts, this is what really led me to believe this rumor) and items og Sith lords had. His main prizes are the helmets of Darth Bane, Darth Revan, and Darth Vader. FWIW, the leaked concept art pictures also labeled the cyborg as the "GRAVE DIGGGER" Now, we've seen him with the Vader helmet, so that's confirmed, and the lightsaber in the trailer definitely has an ancient/old tech feel to it. As some may recall, Revan was set to appear in the Mortis episodes of the Clone Wars..
http://clonewars.wikia.com/wiki/Revan
But George randomly cut it for some reason
... Maybe they had bigger plans?
Anyways that all came out in September.
In late October this came out, of our now confirmed villian
Now anyone who knows Revan, automatically thought of him upon seeing that, but knowing the previous Revan rumors and looking at the quality of the picture I thought this was just some Kotor fanboy spreading this.... Obviously not as this is the villian.
Along with all of that, over the past two weeks, alot of sites have been talking about Revan being brought into the cannon as if it's fact... Disney is still supporting The Old Republic game and Revan is just recently one of like 3 'EU' (along with Plagueis and Mara Jade) characters to still be receiving an action figure.
Alot of reasons to believe this. So he won't be in the movie, but he'll more than likely be referenced.. Opening the door for a spinoff.
It is thought that Driver is under the influence of a 'voice' thats making him seek out these artifacts for a reason. Most likely not Revan, but it's a thought.