Funny thing is, there's actually files for MIDIs that I think were with the original source from :V:. They're absolutely empty.

There are two issues with adding OGG. Well, make that three.
1) Processing time. This would be a problem if you decoded them on-the-fly rather than extracting them on mission start.
2) Memory requirements. In FS2 right now, it's setup to use files loaded into memory that are in PCM format. A 2 minute file will take up roughly 22 MB at 48000hz/16-bit/stereo (CD Quality). In a 128kbps OGG, it would be 1.64 MB. This means a soundtrack would take up 50 MB or more when loaded into memory, if you were using higher-quality OGGs.
3) Coding overhead. At the very least, you'd have to write a conversion function for loading OGGs. If you wanted to minimize memory use to the same size as the loaded OGG, you'd have to write load/play/stop/ff/rewind/etc functions and more for OGGs (This would take somewhat more processing power).
I think the big hold-up right now is lack of anyone with sound experience..