It works, it just needs some special config. The secret is not to use the access key for your server; you need to enter the local ip address of the server plus ":52199".
So for example, if your server's local ip is 192.168.1.1, you'd enter 192.168.1.1:52199 instead of the access code in gizmo. I don't know why the access code doesn't work through the vpn, but it doesn't. Other than that, it works perfectly.