So to be succinct - shouldnt the CM15A see any code activity on the monitored channel?
Yes it should - In fact it should see activity on any housecode. Your V572A (I haven't personally used one) should be no different than a standard transceiver (RR501, TM751).
Oh - I should mention that both Transceivers are working fine and I have no switching problems.
From this I take it that you are able to activate switches via RF and the V572a?
Assuming the CM15a hasn't locked up (try unplugging and removing the batteries for a couple of minutes to reset) you may have the two devices in areas where they can't communicate due to noise or signal absorption.
Try physically moving one of the devices closer (electrically - same circuit or powerline phase) to the other to see if they can communicate. If so, you have either signal absorption (computers, battery chargers, TV's etc), noise (compact fluorescents), or possibly phase coupling problems (combined with either of the other two). You can isolate this by plugging the CM15a back in it's original location and then tripping your breakers until the devices see each other.