(1) To the best of my observation -- and I read Inside Higher Ed regularly -- this certainly happens but it's not common.

(2) AFAICT, when it does happen, it happens through known channels. e.g. there might be a few classes or majors which have a reputation as going easy on athletes, and instructors there might be asked to stay in line.

I'm not saying it never happens, but it's certainly uncommon enough that "grades are meaningless" isn't really true.