With the trend of FF Summons being Primals in this game, I think it's safe to assume Bahamut is a Primal. So Dragon based rules wouldn't necessarily apply to him per se, but it was mentioned awhile ago in a Dev post regarding the End of an Era cinematic (which also discussed the 1.0 cinematic) that the large dragon in the 1.0 Cinematic was Midgardsormr, and was consdered a sort of 'king' among the dragons (or wyrms) of whatever type was featured in the video.

It was also implied that the dragons from the north were/are a Beastribe, like the Ixal or the Amalja.