Can you with a ROS loaded PC with the Dude package, tell it to monitor only a certain ethernet port ? Such as ether1 is a public IP and ether2 is a private/hotspot side and you want to Dude to monitor only the devices on the private/hotspot side. Those devices have static ip addresses and you want the Dude on that PC to just monitor those.

Yes, you can))
make sure, that type of device is RouterOS...
Devece ---> RouterOS ---> Interface ---> <your you want...>