I tried and tried with my serial gateway, and never got it to function porperly. The serial port was working I could see it and data, but OH3 just refused to recognise the data. After a week, I decided to abandon the serial and flashed a esp8266 attached the nRF to it and bobs my uncle as we say. It goes via MQTT, so takes a little more settting up but works fine. If you want more info I will dig out the pages I used to make it work.
Hmmm, the pi OH is running on already has an active MQTT broker. So you got me thinking: Wouldn't it be possible to use the MQTT gateway instead of the serial gateway? It should be able to translate radio messages (Hope RF69 in my case) to mqtt messages which are already recognized by OH. I'll have to find a spare pi and try it.