To be completely honest here, Aeneas, I don't think it makes the least bit of sense to integrate DH into regular Red Orchestra. It goes against logic from a content stand point.
It works for Carpathian Crosses because of what that mod is about. The Soviets remain a major army and most of the environments, weapons, and contexts all apply for that mod. It simply makes common sense to integrate it into RO -- it shares most of its setting and content.
I think of mods like Darkest Hour and Mare Nostrum as "expansion pack" mods. They move the game to completely other theatres of war, where armies, weapons, terrain, and types of warfare change dramatically from the stock game. Integrating something like that into RO would just be plain awkward... it would be like going to see an action movie, only to have it switch halfway through to one of Mozart's ballets or something -- totally out of place and, well, awkward.
Keep it standalone. It makes more sense that way.