I'm not sure. Do the devices "reply" to some specific UDP packets for example? If so one could get the mac-address out of the received replies (not sure exactly how since the info is in the ethernet heather of the packet and std. socket api only returns the UDP data part, not heather info).
If you need lower level stuff like ARP or RARP lNet doesn't provide that at all.
You're basically looking at low level stuff, under lNet's radar.