@King:
How does Cabaji breathe fire? How does Pearl lit himself on fire? How does Kamijiro the lion breathe fire? It's unlikely this is all Haki.
Cabaji and Pearl can be explained as tricks, thought. Kamijiro is in the New World, so I wouldn't discount Holdem having haki.
I just feel a lot of supernatural martial arts are haki related, even if the user is not aware of haki itself. To me, even Luffy, Zoro and Sanji were sometimes using haki pre-timeskip, but they were not aware of how it worked. Only a few people understand the potential it holds.
–- Update From New Post Merge ---
@DatYute:
Then again it also makes no sense that CP9, one of the World Government's most important organizations doesn't have haki despite being handpicked and trained by the Government since they were children, but that's another discussion entirely.
Well, CP9 aren't the top dogs of CP. CP0 are. CP9 are spies and assassins, first and foremost. I bet most of their missions aren't related to strong opponents. CP0, thought, are the protectors of Mary Geoise. Considering Lucci and Kaku graduated from CP9 to 0, maybe once you are strong enough in Rokushiki you can begin to learn the next level.
I feel rokushiki is a way to awaken haki. I mean, high ranking marines are trained in it, and vice-admirals all have haki, I think there's a progression there. Rokuogan feels like flowing armament, Tekkai and shigan feel like armament, kami-e feels like some form of observation, even geppou could be explained as the kicks sending "waves" behind them to walk on air. Maybe rokushiki techniques are just the first steps before someone can truly learn all the potential of haki.