If the world I'm DMing has dragons in it, almost always yes. I'll allow them to use monster classes or to take the Dragon Disciple PrC to get it.
I'm a little peery of odd Half-Dragon combinations, but LA usually takes care of that for me. The most common in my games are either humanoids that speak Draconic (Kobold and Lizardfolk, primarily) or Humans themselves.
I'm thinking of putting together a homebrew, and one thing I'm strongly considering is taking away the Kobold's default alignment and making different clans of Kobolds whose alignment, Favored Gestalt, and culture are based on the dragon type they're descended from.