First and foremost, the OpenVPN option in the UCM is a client only. Not a server. You would need a firewall that supports OpenVPN Server or something like pfSense.
Then, the GSWave would register through the VPN but the VPN is configured on the OS-level, whether it’s iOS or Android.
Once the VPN is connected, the app will register. BUT, if the VPN is disabled, then calls won’t get in since it won’t register to the UCM. I would recommend registering directly to the UCM on secure ports to allow the Android to operate without an always-on VPN.