I hosted there in Nov. and Dec a few years ago, so policies may have changed.
When I was there A loop was opened up on as needed. If reservations were getting close to full they would open it up. Some spots might be closed for maintenance, flooded sites or other issues. They would encourage campers to move into B loop after it cleared out but they didn't force the issue if the camper wanted to stay in that spot.
There was two hosts in each loop with FHU and 10 or so FHU in B loop.
Since the ranger booth is only open limited hours during the winter and there is no spaces in B Loop open simply ask the on duty host and they can contact a ranger and likely let you into A. While I was there I made the executive decision a couple of times to let a camper into A, contacted the ranger and was told to open the loop up.
I don't think anyone was out to inconvenience you by not having the dump station open.
I am sure as an Oregonian you know the Park system receives no tax money and it is supported by user fees, Oregon Lottery profits, donations and volunteers. I'm sure that the dump station will be repaired soon but those things take time. It could be a large problem if the drain field is shot