Without the radio or the SMC gateway device, its a bit hard to help much. Also this forum is for Node-RED running on a groov EPIC system, not Raspberry Pis. You might try the official Node-RED forum over at https://discourse.nodered.org/… That said, have a look at this thread (USB to Serial adaptor support for AR1), it shows how to connect USB devices to groov EPIC, it should be similar for a Pi.
So, you hook the USB to the Pi and the radio. Use the serial Node in Node-RED to communicate via the CAI protocol using a Function Node. From there you just need to know the protocol to get the Radio ID sorted. The IP address of the radio should be the same IP address as the Pi since thats what its connected with.
What is your end goal? To replace the SMC Gateway with a Pi?