The scenario with Channel 5 was even more silly, since Vimeo was just a service that Patreon was using. This not only looked like a shakedown, it was from a hosting platform the group wasn't even directly using.
This may be a much bigger issue than I thought...
I had planned to switch off Vimeo anyway because of the weekly upload limit being so low for my tier (I could tier up but my patreon income is like, 7 dollars so it wouldn't really be worth it). And this is pretty much the motivation I need. It's something I had already messed around with, for the purposes of embedding a custom HLS livestream. And since the only real security Vimeo offers is an unlisted URL and a domain whitelist, my plan was to require actual Patreon Oauth to watch the videos.