Its a rare skill that even a CoA master like Hyogoro knew very little about. It wouldnt make much sense for them to have much knowledge on Adv Haki, much less how to train it.
So no they should 100% know about it. And luffy even without hyogoro's help would have mastered it in 3/4 months just by seeing it once (rayliegh)
Haki has no potential, there is no aura you are born with. Rayleigh said everyone can use it as long as they are aware of it...
What rare skill....it is not like coc that you have to born with it...