The man is still a coward and a traitor. Using his shout only proves one thing: The man is a coward that didn't dare to fight honestly despite being older, stronger and more skilled. What he did was technically legal by Nord laws, but most people see it for what it is, a dirty trick.
Also, he is still a racist. If he really cared for "independence" and "freedom for the oppressed" he would support the forsworn against the Nords. Not to mention that the Nords have no right to the land of Skyrim at all, it all, rightfully, belong to the Mer.
Anyway, the fact that he used his Shout to fight the king, makes it oh so much better when you shout him to death before he has a chance to open his mouth or draw his weapon in the final fight...