Please, allow me to rephrase your current setup.
CentOS7 for “home server” and “VPS server”, with wireguard installed. And NethServer 7 on top of that.
Now…
NS7 did not used in any way Wireguard, but into NS8 is built in for allowing comunication between master node and workers nodes, so actually is already taken and controlled (more or less), so i dont’t think that currently the sysadmin could/should really mess with that).
https://docs.nethserver.org/projects/ns8/en/latest/cluster.html
Also more than 1 year ago was stated that OpenVPN is not actually into plans
But this might have been changed in recent months, IDK.
With current informations and as far as I know, from official documentation
https://docs.nethserver.org/projects/ns8/en/latest/
or the wiki (more or less currently a draft)
https://wiki.nethserver.org/doku.php?id=nethserver_8
your setup must be crafted from scratch and manually at OS level (Debian or other supported distro for NS8), I don’t know if the backup procedure of NS8 can take care of this personalization.
However, you can consider to add something else as tunnel between your installations: Tailscale or ZeroTier probably could be an option for your needs.
Otherwise… I don’t know if the master/slave communication infrastructure (Wireguard) between the nodes can be repurpoused for allow also communications between containers in different nodes. Again: I don’t know