Quick update on this topic:
Okay, I've tried it out; Converted an .mptm song to .IT format; dropped it into my project and there are some issues. If you're interested on my findings regarding modules in unity, read on...
Unity apparently supports .MOD .XM .S3M and .IT formats... Here's why:
Firstly the Unity engine uses FMOD for module support; needless to say, the module used didn't quite sound right in-game. Some samples, volumes and effects were a bit "off" but it would be passable if I worked around it with my composition. Seems to run good on the PC, I still have to compile and test on actual hardware to find out about the performance hit.
Next is file size. Unity's Module support would go a long way if you were using formats that would save space, such as old school MODs or other formats where you use fewer tracks, or if you are using only a handful of short, simple samples but in my example, My Module was almost 26MB, way larger than if I were to convert it to an MP3, which would probably be less than 3MB (almost 10x smaller)
However, if you keep your modules small, you can use scripting in the game to do things like change track volume, or enable/disable tracks, etc. although I'm still looking at the docs to find out how to use these features. This could make for some interesting in-game features.
However, Seeing as to how playback is not accurate to how I intended it to sound, and the smaller size of an MP3; it looks like that's the route I'll be going. At least if I mix it to an MP3 in OpenMPT, it will preserve all the VST effects and playback will be accurate, not to mention make the final APK smaller.
Maybe I'll try to make some tiny modules for certain parts of the game where the track loops and such, while other parts use MP3 files instead.
Just thought I'd share my experience with this so far. Feel free to share ideas and input on this; I'm all ears!