This is assuming that their room has excess occupancy available, and the OP isn't on the dining plan. If on the DP, adding him to the room will be quite expensive as everyone in the room has to have the dining plan.
If you can't add him to the room, then technically he isn't allowed to visit SAB or any other pool. Whether the CM's choose to enforce that is hit or miss, though SAB is by far the most thorough with the room band checks.