On fiddle set up, the bridge is often flatter when the fiddler plays in a style with lots of double-stops. (2 strings at once) Not all fiddlers have their bridge flattened because they don't all use a lot of double stops. Even classical players with classical set-ups play double stops. My guess is that a lot of bluegrass fiddlers play with a flattened bridge. Still, it would be good to have a knowledgable teacher explain set-ups.
I'm of the opinion that no learning is wasted. I've heard the comment that being able to read music somehow hurts. No way! Being unable to learn by ear, and relying solely on sheet music does hurt, but learning by ear is the way we all start learning music. (I don't recall anyone passing out sheet music for those playground songs, camp songs or the ones we sang on school busses, and just about everyone sings along with the radio.) Someone learning an instrument simply has to transfer the ability from voice to instrument.
The best teacher would be one who understands bluegrass very well but knows about other fiddle styles. Music involves the cross genre-isation of not just tunes and instruments, but techniques.
On starting out with a classical-only teacher, I still think that a kid who wants to learn bluegrass because he loves bluegrass would get very frustrated at being made to learn something else. If someone had forced me to play scales when I started learning, I may have become a better player, but I most likely would have quit before that happened.