THAT'S how you use pre-existing music to score a scene.
You can play ANYTHING to Freebird, as long as it's in slow motion, and it will be the shit. That had nothing to do with the directing. Try it. Fuck, you can
walk in slow motion to Freebird and you won't feel stupid.
I don't think its fair to compare his directing style to typical slasher movies like Texas Chain Saw Massacre or something, because the character development in those movies is crap compared to Zombie's movies.
That's because the whole point of the genre is that there
is no character development. The reality is, that just because a guy (specifically from Devils Rejects) makes a funny joke or two, that doesn't make him a likeable character. Do you honestly "identify" with cutting off peoples faces and wearing them as masks (where have I seen that before)?
No.
But the dude makes a funny comment in the movie and you're going to tell me that you "identify" with that character all of a sudden?
Rob Zombie is good at finding out of the way, dirty, old locations for his films. Or perhaps I should say... His location scout is good at finding his out of the way, dirty, old locations. The film stock gives his movies the feeling, not his directing.
Edit: Also, if you want to talk about "pre-existing" film score... Watch a Tarantino film.