The way it was explained to me during my instrument rating (in a G1000 C172) was the displayed identifier does count as properly IDing the navaid. You still could listen to the audio to supplement the display, but it's not a requirement unless the ID doesn't show up on the PFD for whatever reason.
Hope this helps,
- Paul R.
A more direct link that aburley pointed you to is here:
http://forums.vrsimulations.com/support/index.php/Navigation_Systems
If you are interested in how other military aircraft (outside of MSFS) navigate, you can check out the flight manual for the A-10 here: http://www.digitalcombatsimulator.com/en/downloads/documentation/
If you'd like to see an actual flight manual for an A-10A, you can download it here (the internal navigation computer stuff starts on page 1-91 or 115 if you go by the acrobat counter): http://www.476vfightergroup.com/downloads.php?do=file&id=42