Correction: several stock sounds found in ArmA2 can be called from within your mission, without redefining them in your description.ext. The problem is finding references to them, so you can call them. I know only a few so far (that are being used by the High Command module). You can test them yourself in the editor:
player say "hc-001"
player say "hc-002"
player say "hc-003"
/.../ et cetera /.../
player say "hc-079"
Or why not try
playSound "LHD_engine"
The first are high command orders and respones from your troops (in broken english). I believe there's a "MEDIC!"-sound among them. Or words to that effect. The second eexample is an engine sound intended for the carrier ship. It's used in the campaign to give you the feeling of being onboard a moving ship. The examples above are all in .wss format. To find more sound sources inside ArmA2: unPbo the addon missions.pbo
It contains all scenarios from the SP, MP and Campaign sections in ArmA2. Browse through the scripts that comes with these missions, and you should find a plethora of sounds that are being called from within the missions. It's hard and tedious work, but well worth the effort.
Please share your findings