Just a general remark:
In Domoticz currently the HA AutoDiscover function is being implemented (still in Beta but almost finished).
So it should be easy now to connect devices through OpenMQTTGateway as it is default enabled Advanced configuration of the gateway | OpenMQTTGateway v0.9.9beta
Domoticz documentation for AutoDiscover:
https://www.domoticz.com/wiki/MQTT#AutoDiscover