I had the same questions. I am a homeseer user and want to explore openhab, but I don’t want to buy a new Zwave adapter (and rebuild network) or put my radio in my garage with the rest of my gear.
The homeseer znet does not run a home automation controller of any kind, it is purely a Zwave radio with an ip based interface to pair with homeseer over IP.
It is similar to the iTach IP-to-IR/Relay/RS232 that provide a generic IP interface to whatever they connect to on the other side. I have an ip-to-rs232 connected to the management port of my security system, far away from my Zwave radio or home automation controller
I guess the general confusion and disbelief that such a product even existed answers the question on whether openhab supports it.
It would be great to extend a Zwave network purely over IP to allow for non-connected buildings, or vacation homes, or cloud based controllers to be possible without needing to home openhab directly with the Zwave radio