Sure, why not?
I do have a question though. Where is the relation between making RPG's and MMO's? I ask because, in my opinion, MMO's aren't RPG's. Even in most cases where they're referred to as MMORPG's they're not RPG's. Most MMORPG's basically consist of loot treadmills and group challenges. People play them to acquire more better shiny toys and work together as a team to overcome the latest available obstacle. Very few people, if any, play them to "role play" a character. There are exceptions but, for the most part, this has been the truth of the matter.
Why do I bring it up? Well, a single-player RPG, even if it has some multiplayer capabilities, and a MMO are very different concepts. I don't see how a developer being good at designing one would translate to the other. It would be like expecting your typical FPS developer to be good at designing a RTS. They might be able to do so. They might not. There is no reason to anticipate success or failure in one game type based on another.