Answers:
1-What does it mean to have a microphone wired "Dual Mono"?
What we call "Dual Mono" is a mono microphone that has it's
signal sent to both contacts of a stereo plug, so that it feeds both
channels of a stereo microphone input jack. Typically, this is a stereo
1/8" (3.5mm) mini plug.
2-Why would I want this?
If you are recording with a mono microphone into a stereo recorder,
and would like to hear what you recorded on both channels upon playback,
you would want your microphone wired "dual mono".
You don't want to do this. Plugging into a mono recorder would short
one contact to ground and the mic won't work properly and you risk
damaging the mic and/or your recorder (although the risk of damage
is remote). If you plan on using a mic with a mono recorder, don't
get the "Dual Mono" version.