Also adding, given you are in CA I don’t think that another visit (or any visit at all really) would be expected even with a RD application.
There may well be some things your S can do from CA to confirm his choice and (if desired) show additional interest (again, ED is the most important show of interest as far as the school is concerned) – see if there are online tours, get on the email list, ask if any admission officer is doing a presentation out in CA, ask if alumni interviews are available etc.
Sounds like Bates is a great option for your S and I hope things work out for him.