Yes, your child needs to learn to stand up to people like this. Part of that could be talking to the RA and/or the counseling office.
Is it wrong for your son’s roommate to be domineering? Yes. But a big part of the issue is also your son not willing to advocate for himself and make attempts to nip it in the bud. It’s a good life lesson to learn. He needs to start by seeking assistance if he doesn’t have the skill set to do it currently.