A couple of thoughts come to mind. One, it depends on the thickness. There is usually some rust or dirt there anyway, so if its not excessive, probably not a big problem.
The other thought is, if this is not going to be a show vehicle that is never driven on the street, thats fine. But if you drive it normally, get ready for some bad smells.
I know you bake powder coat on at about 400, but brake drums can get a lot hotter than that briefly during hard braking.