OSCII-bot could be a useful means of converting Midi to OSC outside of your "Midi controller" and sending it on to Reaper without being dependant on complexity and features needed in the controller.
Otherwise, to do OSC, the hardware controller and its embedded software needs have all of
- a suitable interface hardware and transport mechanism for OSC
- the means of running (executing) a suitable OSC protocol library (to make the IP addressing and UDP implementation expected by Reaper easy)
and
- a means of editing and configuring the OSC strings to be suitable for Reaper or some other OSC target
This thread might be helpful
https://forum.cockos.com/showthread.php?t=181561