Well, he has fur and a wolflike face, doesn't he?
Aren't dragons supposed to be repitilian, and
have scales and wings?
And breathe fire?
How the heck can a dragon stay in the air
without wings?
Haku is based off of the Asian idea of a dragon(seeing as the movie is created by Hayao Miyazaki, a Japanese animator, and was later translated into English and dubbed by Disney). Much different from the Western idea, Asian dragons tend to not have wings and to be very beautiful. They are considered good spirits rather than evil. If you look a picture of a Chinese dragon, Haku is very similar to one of those.
Also, to be honest, I'm not sure it is said if he is a dragon at all. I know that he is the spirit of the Haku River, and may simply be a creature of Miyazaki's imagination.