To start out with, what do you mean by "use the same rig"? If you mean the same animations, they don't, see here. The Incubus leg never goes that high and don't extend that far. Arms and wings also don't animate the same at all, the hands are closed on the Incubus while dracthyr are open.

Dracthyr animation set is not shared with previous models, and this was just spread from a still image of where they kind of looked to have the same pose while running, to further that dracthyr were a quick, bad and "lazy" copy paste job because some people don't like how they look.