Elementally, fire (red/traditional dragon), air (sky blue/coldness), earth (brown?/burrowing) and water (aqua/somewhere adjacent to seamonster) and possibly fifth/sixth/seventh/etc elemental variants (spirit, time, fate, life and death) would be what I'd be looking at if creating a 'dragonable' universe. Not sure if these could fit in with DF, though.
I don't know if the 'healing' dragon, as mentioned would merely be a tamed one that was capable of also removing life-force (prior to training, or to Dwarven enemies after they have been) as part of its raison d'etre, but a megabeast wandering round healing anything that it met (unless recognised as a 'nursemaid fish' by everything it could ever encounter, or perhaps being a natural denizen of undead plains, being 'anti-deadly' to those undead and converting them to non-animated corpses by its powers of life-control) wouldn't really get very far in the world.
It really goes for them all. For a given environment, their 'flavour' should make sense. A dragon that turns cretures to gold with a glare from its eyes? It's a metallic creature that has developed the trick to process organic material into something that it can imbibe. A sleep-inducing dragon? Possibly one that is itself intrinsicly sloth-like and it's a skill it has to level the playing field in an environment where there's not much to eat, but what it can find is usually too quick for its low-metabolism movements to let it catch.
Something like that. As a principle, while probably not an example, at least.