Looking for montoring of OpenVPN server

I would start here: https://openvpn.net/community-resources/management-interface/

There is an example of how to use this (not in an LM-friendly way) at https://kifarunix.com/how-to-monitor-openvpn-connections-using-openvpn-monitor-tool/

There is also an example (a bit dated) on how to expose data via SNMP here: https://github.com/Phhere/openvpn-snmp

The problem seems to be a general lack of standard monitoring since OpenVPN runs on so many platforms.  If check_nrpe works, perhaps just punt and use that via an LM script datasource :).