I suspect strongly that this is against our monetization rules (unfair advantage of high slots for paying users) and recommend to report the server via the contact form at https://www.bohemia.net/monetization. However, the team over there will make the final decision.
General rule is:
If you encounter a server offering monetization, that is not listed here, report it to us. They are breaking the rules, any monetization needs to be approved by us.
Even if a server is listed as approved, if you are under the impression that the monetization is against our rules, you can still report it. They might've changed their monetization system after being approved.
This is allowed under "Charging players to access your server", and gameplay cannot be affected if a player is not on the server.