I have found out here that we cannot have SignalK nodes in Cerbo’s NodeRed and that SignalK embedded NodeRed will not have Victron nodes. 
As I do not want to have two NRs running on same system, I was looking for alternatives.
I have found signalk-mqtt-push module that can push specific SignalK property into Cerbo MQTT. I have configured it to push propulsion.port.revolutions to MQTT and then I can use MQTT In node in NR.
This is my test flow:
Need to test it further to see if I can integrate it with my heater automation flow.