Ok, having had time to re-read your concern/bug, I have the following points
1. Viper has the ability to listen to 1 TACAN and 1 ILS only
2. The default TACAN (unless changed in the ME) is 1X. There are no map gnd stations on 1X
3. Likewise, the default ILS is18 something, so unless you’re near a single airfield with that ILS freq you won’t hear the Morse.
4. What I suspect is actually the case, is you are flying on a server on the Caucasus map and are in actual fact, hearing all the outer and inner marker beacons for the airfields. This is a DCS bug, in that ALL marker beacons will be heard. IRL. This is nothing to do with TACAN or ILS.