Interesting, you think Dean is an xSTP? I think he plays Dean as an ESFP more then an xSTP. He becomes more xSTJ like in times of crisis. But overall Dean seems to me to be a feeler, he is all about keeping his family together in all situations. He says his father and brother are the most important things in his life and all he really wants from life is to be around them and make sure they are safe. In times of stress he does represses his emotions until they get the best of him but he is generally a pretty easy going guy.
That being said he has played other xSTP characters. You could argue that Alec/Ben from Dark Angel could be seen as an xSTP character. I would say his Dawson Creek and Smallville roles seemed a bit more J based though from what I caught of them.