The Active partition had disk corruption. I suspect from our backup, but I don't know for certain.
It turned out that our previous Active image, which was from version 6.4.7 was on an entirely different disk. The server is old so I still had one of the legacy disks left in the VM.
So the Aruba tech decided to give that image a try. He set it as the Active image and the machine booted up without a problem, just beind on verisons. He "removed" it from the cluster, since it had been droped from the publisher already. We then performed upgrades on it to get it running the same version as the publisher, then we reformed the cluster.
Everything was okay after that.
Very strange, I wish I knew for sure what caused the disk corruption. Thankfully though we had that other disk that was somehow untouched.