Is this an IPSC system? I have had two different scenarios where repeaters on an IPSC system would not show up in RDAC.
-The first is when the repeater is functioning fine (repeaters local RF, repeats WAC, can be pinged on the local and remote LAN). If the UDP port programed into the repeater is not unique (because its used by another repeater or by RDAC), RDAC will have issues. Change the UDP port to a unique number and the issue was resolved.
-The other scenario is the repeater can be seen on the network via ping and LAN switch logs, but wont show up in RDAC. Also passes very poor WAC audio. The network card was locked up (but would respond to ping) and required a reboot. That was a bit difficult to troubleshoot remotely because the symptoms made it appear that the repeater was fine and the network had issues, but that was not the case.
Hope this helps give some troubleshooting ideas.