Last I tried you could download native gimp, but it was fatally flawed in its keyboard handling. Nice progress, but still more work to go. It's been a while since there was an update, so no breath holding.
Up till now, the "native" Gimp still used X11 (which is being worked on (see Xquartz), but still buggy) for OS X. And X11 isn't exactly native on OS X by any means.
