Yes, it’s allowed and encouraged between RED<->OPS. There are a few tools on the RED and OPS forums to automate most of the process (e.g. Transplant, REDCurry, Takeout, Orpheus-Populator, etc.). Cross-posting torrents on many sites is allowed and fine, you just have to be aware of the rules of the source site, e.g. some places don’t want their internals to be shared, or some have a literal timer countdown before cross-posting is allowed. On the other hand, most sites are not going to enforce other sites’ exclusivity demands (PTP explicitly has a note about this). If an exclusive file is cross-posted onto PTP, PTP isn’t going to take it down on anyone’s behalf.

I’ll note that private tracker culture has warmed up quite a bit in the past decade and a half that I’ve been on them. Trackers (and their users) don’t usually see other trackers as rivals/competitors anymore, release groups are respectful of each other, there are a ton of tutorials and help forums around to help low-skill members learn how to do the advanced stuff, and so on. There are recognizable usernames everywhere, and the general vibe is to cross-upload as much as possible and help build everyone’s trackers together. Cross-seed (the program) has helped a lot with this, and seedbases have become very strong even on smaller trackers as a result.