Don't know if it's a bug or inteded, but you can get more than one dragon per structure. If the temple you built falls in enemy hand, the building get destroeyd, but the "resource node" do not. So if you recapture it, you can build a new temple for a new dragon.
The Ashwaken Dragon is awarded by a quest chain. But he's vastly inferior to the Storm Dragon you get from research. They are still both really nice for city sieges, Overpower + Flame breath is a nice combo with lot of units around 