Given the dragon in the background, I do think it's supposed to be Ryuma. Just Ryuma circa the time of the Monsters one-shot in Wanted, before he got his scars. "Zombie Ryuma" isn't quite the same character, so it makes a little bit of sense for there to be two of him, sorta.
We could have some fun with some other scenarios, though.
It could be Mihawk. The eyes are wrong, but it kind of fits his spiky hair. And the flames are obscuring if he has sideburns or a mustache.
It could be V Nusjuro in his prime. Before he went bald and needed glasses. I doubt that's what Oda was going for, but it would kind of work.
Or if you want to get really crazy with it, it could be a VERY early prototype for Garling. Kind of like Kaido's original silhouette, Oda may have changed his mind about designs as time went on. He might have had the idea for the character, but didn't have his final design ready, yet.