Can you elaborate on this at all? I connect to an OpenVPN server while behind NAT all the time and it has worked behind almost every possible network configurat

Can you elaborate on this at all? I connect to an OpenVPN server while behind NAT all the time and it has worked behind almost every possible network configuration I've tried (no NAT, "home" NAT, carrier-grade NAT, cellular data, etc.). If you want the best possible reliability, run the server on port 443 with TCP (even though UDP is almost always better for performance since TCP over TCP is icky). You have a much better chance at not being blocked by firewalls, and it actually works on a lot of the less-sophisticated captive portals without first logging in. (Granted, the article is talking about using OpenSSH and not OpenVPN—but I suspect that should work fine behind NAT as well).