Well, in canon, he has no time to manifest and interact with anyone because he is too busy fighting off horrors at the bridge metaplane from Harley's back (it's not like we didn't do that already!
).
However, as a spirit, since he is an ancient great dragon and (former) dragon loremaster, meaning he was likely the single most well educated magical entity on Earth, he could have any powerhe wanted to. As dragons go though an astral-only phase in their life anyway, gaining spirit foprm is easier forthem than for flesh-bound metahumans, hence his dragon attributes should enter into the spirit form, too.
When used with masking, given that Dunky was a nth grade initiate (n =< 200), he could pass as any kind of creature whose form he chooses to assume. Yes, theoretically, you could make a roll to see through that. But realistically? Ahem.