I remember some MIDI apps for OS/2 have been around. Including (I think it was called) MIDI station.
This page is " alive" but the download links are not working.
http://www.sainthelenapark.org/Subweb1/MidiLab.htmIt mentions all sources are released (link to ZIP does not work).
Here you can find some MIDI programs
http://kimludvigsen.dk/os2/os2/sound/index.phpI just did a VERY VERY quick search on google. Try hobbes.nmsu.edu as well.
As to OS/2 playing MIDI files, support for reading the MIDI files has never gone away from OS/2. Its just that for many PCI chipsets, hardware synthesizer support was written. Just about all PCI chipsets never supported MIDI play on OS/2, with the exception of 2 or 3 cards. . Thats why Timdity is now recommend as a software synthesizer.
If you want to use MIDI devices on OS/2 such as a MIDI keyboard. You have two options.
1. Use an old ISA soundcard.
2. See if you can do something with USBRESMG.DLL and/or LIBUSB to port something from Linux.
Since all MIDI adapters these days I think are USB to MIDI converters. It might work with USBLIB as MIDI does need that bandwith a driver might not even be needed.