Nope, these are not racial hit dice, just some extra hit points. So you don't get any skill points, or feats, they don't count toward your character level or anything like that. And these extra hit dice don't get increased with the half-dragon template.
Generally there are not chromatic dragons on the side of the rebellion, though the occasional chromatic half-dragon is. They're pretty rare though, as most chromatic half-dragons with half a brain can get a very comfortable position (and most have them from birth). But you do see the occasional gem half-dragon in the rebellion as well as the metallics. A chromatic half-dragon would be fighting constant suspicision at best and outright attacks at worst if he were to join the rebellion. But there are a few. Very few.
