Hi,
I don't know how your setup looks like and in what you are testing (internal or PSTN call).
If you hear nothing, you can say at least that..
-CUCM is configured properly for MoH (or else you would hear tone on hold).
-If you see that the router sends traffic, it probably does
You don't mention if you don't hear MoH in a 1) IP phone to IP phone call or 2) with a PSTN call.
If you hear MoH on the PSTN but not on a IP phone, make sure add a loopback and add the IP address of this loopback to the multicast statement in the SRST config.
If this is done, make sure that you have the phone and the router on the same subnet or multicast routing enabled.
/Martin