Olimex Ltd. ESP32-GATEWAY

Do you know if the Olimex Ltd. ESP32-GATEWAY card can be integrated?
Where can I find documentation?

Well since it is an esp32 and has wifi you should be able to use MQTT (look at the pubsubclient library) to have your code on the esp32 talk to NR.

Do some google searches using 'esp32 node-red' and you will find many tutorials you can start off with.