The Dink Network

I'm pretty sure it's only .midi. Now I could be wrong about this. Though if you wanted to check real quick you could pop open your dinksmallwood map editor make a new dmod, put a .ogg in the sound file, call for that sound file, and then test your dmod and see if it works.

You can also use .wav files, so maybe you can use .ogg for sound effects, but I don't think you can use them as a replacement for the .midis.