NMS sends MWI signaling over a D-Channel. If you have a point to point PRI providing tie lines between 2 systems, then you can use it to send the messaging.
In an environment where the systems are tied together using virtual trunks, then the NMS messaging is sent out of the system hosting the CallPilot, and the NRS determines which system to deliver the messaging to based on the routing entries for each endpoint.
So the answer to your question is no. you cannot use an ethernet port for NMS.