It's a new model. The existing NWN2 dragon models are for red and black dragons - the new bronze model is more similar to the red dragon model, but they all three are different models. Like NWN dragons, their differences are mostly around their heads and dorsal ridges. Though I will say the black dragon looks a lot different than either the red or bronze.
About parity with the 3rd edition art: I'd also say the red and bronze look more similar than the black (as in the game), and that the art in the game obviously tried to stay true to the art in the 3e books.
-Throbblefoot
