Promised I would get back to you once I moved my Zigbee2mqtt server from windows to HassOS using my Eltima virtual port over LAN.
How?
On Windows10:
- CC2531 hardware is connected to USB (COM8)
- Eltima setup as comport server on TCP port 5656, with settings com8, real port, 115200 baud ,No parity,8 data bits ,1 stop bit
On HassOS (running under Hyper-V on the same W10 machine)
- Installed Zigbee2mqtt HassIO Add-on (from repository GitHub - zigbee2mqtt/hassio-zigbee2mqtt: Official Zigbee2MQTT Home Assistant add-on)
- Edited serial: share\zigbee2mqtt\configuration.yaml:
serial:
port: 'tcp://192.168.1.22:5656'
I also copied the database.db from windows to HassOS share\zigbee2mqtt\database.db, so I did not have to re-pair all my devices again 
Major advantage by having zigbee2mqtt (including its configuration) on HassOS is that it is now included in HassOS snapshot, making the maintenance & recovery a hell of a lot easier 
PS: ofc you also need an mqtt-broker