I wasnt sure to be honest if the actor who played Stevie was really disabled or not, as I've never seen him TV or any other programs... so wow. You learn something every day.
(Maybe the crazy robot machine in Reese vs Stevie should have given it away *doh*)
No, Criag is not disabled nor does he talk the way that Stevie does, in real life. It's a credit to his acting ability how convincingly he's portrayed Stevie all these years.