Rabbit is adopted.When his partner asks him what ethnicity he is, he quickly changes the subject. It's hard to understand why he would be ashamed of being Maori, or Samoan, or Arab, or whatever. The answer is that he doesn't actually know what ethnicity he is - he was adopted at a very young age and knows nothing about his birth parents.
The show is set in the same Limbo as the final season of LOSTIt can't be a coincidence that Christian Shepard is also a doctor on this show. Obviously Rabbit and Nancy actually died in the helicopter collision and they have to learn to "let go" in the same way the LOST characters did.