No, he's not unlockable in Street Fighter 4, sadly. But he's going to be playable in the oddball Japan-only Street Fighter Online: Mouse Generation, and it looks like he can sling fireballs with the best of them.
Sporting a debonair tuxedo and cartoonishly big teeth (yeah, I don't know), Obama seems like a force to be reckoned with in Street Fighter Online. You can make him say "YES WE CAN" in a gigantic word bubble, and he's got a standard fireball attack too. He also looks like he's been training with Balrog - Virtua Fighter 2 looking graphics aside, this version of the Commander In Chief is decidedly beefy. He'll be arriving in the game on Valentine's Day as part of a promotion that also includes playable chocolate figurine chracters and a Zangief who has what look like clam shells for shoulder guards?
If you really want to play as Obama in a fighting game, I'd say dig around for the inevitable MUGEN version with Obama as a character, possibly as overpowered as Omega Tom Hanks. You probably do not want to play Mouse Generation. It's online yes, which is cool, but it's also a Street Fighter that is solely controllable using your mouse. You left-click to punch, right-click to kick and swoop around your mouse like a fool to do special moves. The character models are based on action figures, and body parts can be swapped between them (like action figures) to make customized characters. So, Barack Obama torso and head, Zangief arms and Chun-Li legs? Yes, please.
Now, as for the real question here: Is this racist?