Sounds like a very restrictive tracker... but I guess the more restrictive, the more likely it has good stuff. Seems kind of strange though because most trackers I have seen just completely ban any sort of proxy or VPN.
They usually ban VPNs for website use but allow them for seedboxes (sometimes requiring approval). The rationale is to stop account sharing and ban evasion.
I don't know but it's pretty suspicious to ban VPNs to use something that is illegal in many countries. Hope they don't keep records that can be leaked.
It's really not. Even if they aren't recruiting new members you can buy an account or invites. You could also prepare alternate accounts ahead of time.