Did you succeed with OpenVPN between proxmox hosts at Hetzner?
I am trying the same thing,
But first I wanted one proxmox 5.1 host's openvpn to connect to my existing openvpn server.. (and when it works, between different proxmox hosts)
But every time I try to connect the vmbr0 to the eth (enp2s0) interface, the network will not start correctly after boot.
If I add the binding in the host after boot (like iptables -t nat -A POSTROUTING -s '10.64.12.0/24' -o enp2s0 -j MASQUERADE ) I can without problems access the internet from a guest.. but try to do it inside the network/interface file, seems to lead to some kind of network misbehaviour when booting the host (even the enp2s0 Ethernet IP is not accessible from outside), and I have to reboot in rescue mode..