I doubt the title of King or Queen carries the same symbolic significance within the White Court that it has in the mortal world. It might not be anymore significant than calling Al Capone the King of the Chicago underworld during the late 1920's. Yes, he was the most powerful criminal boss at that time, but he wasn't a king in the true sense of the world. Also, has anyone aside from Harry ever referred to Lord Raith as the King of the White Court? I'm not sure. Even the title of Lord, in Lord Raith, might just be an acknowledgement that he is the accepted leader of the White Court.
Then we get to the nature of the White Court itself. Initially, the rest of the White Court are going to see Harry as nothing more than Lara's playing and her food. Should the marriage occur Harry might have to pretend to be nothing more than that so Lara doesn't look weak and invite challenges to her rule. (That could be fun. Sort of Like Zorro pretending to be an over privileged, lazy and cowardly weakling. However, Ebenezer and other members of the Council might believe it was true.)