I think the dredlords should appear in the regular game outside of the campaign. In the origional game they usually added a lot of flavor and difficulty to the game when they appeared, they had vastly superior weapons technlology and always added a late game challenge. I think they should be added to this for the same reason, and why not give htem unique technology that can be stole, for example, to add some of that kind of flavor to the game.
Of course their being in should be an option but it would add some interesting elements to the late-game if done correctly.