User blog comment:Feroza/How will Luffy awaken. THEORIES./@comment-26058050-20161018144824/@comment-26058050-20161018153254

From what I understand, Rayleigh taught Luffy how to use Haki, and Luffy incorported it in his own fighting style (as Luffy does normally) and I think that's all he taught him.

I like to think that Roger didn't have a devil fruit, a man who was capable of taking on the world and conquering the grand line without any devil fruit powers, that's someone who is truely worthy of the title. If anything, I imagine that he had haki powers like Rayleigh and could use them on a totally different level to others.

You do bring up a good point with Sengoku however, very few people (even in the OP world) knew that he had DF powers, and he is a solid argument to point out that he could just be hiding it.

As for Garp hiding the truth, well a couple of things come to mind on that. 1) He wasn't always around. 2) Even if he told him, Luffy probably wouldn't understand or care. 3) He would have had to told Ace about his heritage, if Luffy asked the same question, he'd probably would have told him. 4) Being part of the plot. Common scenario where they just drop a "WTF did not expect that" into the story, just to build character relations.