As long as private trackers have absurd seeding rules and require you to sign up (initially) without your VPN active, I won't be touching them with a ten foot socket.
From what I have seen about published seeding rules most trackers as switching to pretty reasonable rules. Typically the only major sin is not seeding for a minimum length of time (usually a few days). Then there are ratio rules but these are typically assisted by bonuses for long seeding even with no downloads and freeleach for new and popular torrents. There are still a few trackers where the site ratio stat is zero-sum but for the most part this isn't the case. As long as you do make content available you will not be punished.
I think they mean join a group that uses a shared Plex server. People sell slots on their own servers with an automated/semi-automated request workflow for new content.
People running such trackers usually have no idea about security, they‘ll likely put your IP in an excel sheet, for law enforcement to take when their home is raided.