Most community servers don't allow VPNs, because it can be used for ban evasions and other issues. Plutonium has nothing to do with it. It's up to the server owner.
I've also been banned for cheating/exploiting from re4l but in black ops 2. The only problem is that I wasnt even remotely hacking due to how many times I've died in the match. I'm starting to think the re4l is just handing out bans for absolutely no reason at this point.