Some old Reddit users say that it was indeed possible to add people as moderators without their consent

Can confirm, that's how I got put on the modlist at /DoesAnyoneElse for a spell. Someone figured I'd be a good hand on deck, hit the "add" button, and suddenly my mod queue was filled with a lot more bullshit than it was the day prior. I had to go hunting through their modmail to figure out if I'd been added deliberately or in error.

Just ...

I tried looking for some archives of the subreddit and spez's account, however I didn't find anything that helpful. I only found two archives on archive.is from 2010 and 2011 (which I'm not gonna link here for obvious reasons), and the moderator lists didn't include spez.

That also checks out with my recollections. I was pretty involved in some of the calls to get /jailbait taken down when it first came to site community attention, so while I'm open to being wrong - I feel pretty confident that it would have been something we'd talked about at the time if he'd been there particularly long or was particularly active.

As a somewhat separate point, I think VA - head mod there, among other places - would absolutely have burned Spez on the way out if Spez had that sort of clearly voluntary connection to the sub. Reddit had encouraged him to be there, then hurled him under the bus the moment national press caught wind of the sub's existence.