I don't think he will do well at OLB, he has good size but he is a Safety. He has had trouble covering but this has been a bad year all around for the USC defense and last year in a good defense he was a top 15 prospect. I think some team will love his size late in the 1st round and try to improve him as a Safety. Personally, watching him, I think he can be a very good Safety if coached well.
I myself haven't watched Mays, but have read there are some serious concerns about his ability to cover & to find the ball as a safety. There is even some discussion of a move to OLB at the next level.