In regard to hillbillies, notice what Bob Dylan says in this second paragraph in his description of rock:
Traditional rock & roll, we're talking about that. It's all about rhythm. Johnny Cash said it best: "Get rhythm. Get rhythm when you get the blues." Very few rock & roll bands today play with rhythm. They don't know what it is. Rock & roll is a combination of blues, and it's a strange thing made up of two parts. A lot of people don't know this, but the blues, which is an American music, is not what you think it is. It's a combination of Arabic violins and Strauss waltzes working it out. But it's true.
The other half of rock & roll has got to be hillbilly. And that's a derogatory term, but it ought not to be. That's a term that includes the Delmore Bros., Stanley Bros., Roscoe Holcomb, Git Tanner and the Skillet Lickers... groups like that. Moonshine gone berserk. Fast cars on dirt roads. That's the kind of combination that makes up rock & roll, and it can't be cooked up in a science laboratory or a studio.