You can forget to tune the NDB feq and still do the approach in the Airbus. You can delete the NDB freq from RAD NAV and still do the approach on the FM. In fact, even if the ground sation is not working, you can still do the approach (not according to the reg's I know).
The aircraft will follow the green line from FM in a managed lateral navigation and will follow the vertical profile if indeed fully managed.
If this approach was done fully selected in both laterally and vertically, then the NDB would have to be tuned and the needle followed in Track/Flight path.
This is indeed very seldomly done, very seldomly!
Airbus has many ways to skin the cat and sometimes this cat bites back as Tiger if you screw up. This looks like one of those cases where procedures were not followed and systems not understood. Autopilot will disconnect at MDA minus 50ft, and then Airbus says you're on your own for what ever happens next.