this is a good question that I'm also interested in.
I'm assuming at the very LEAST one should NOT use a VPN when engaging in any buy/sell/trades of invites. But one would THINK VPN usage shouldn't harm anything if one is just posting, participating here. Logically, I would assume the no VPN usage is a protection for both buyer/seller and traders in case there is ever a dispute so there might be some redress if something goes wrong.
But don't quote me on anything above, just speculations. A 'rule' should be respected, and its good to ask for clarification if there are 'exceptions' for VPN usage.