Yeah, being unusually short doesn't disqualify Dinklage from playing Trask. That'd be just moronic. The bloke is clearly a great character actor and I look forward to seeing him in the role.
I was actually pleasantly surprised when it became apparent that Dinklage *wasn't* going to be playing a mutant. It actually feels appropriate that they've cast someone who's condition usually restricts them to playing fantasy type characters (aliens, goblins, miniature clones etc.) and given them a role that (presumably) has nothing to do with it. Given the themes of the X-Men franchise, I wonder if theyr'e making a point with this? Either way, bravo!