Currently OSC can't be assigned in the Edit Go Triggers dialogue, however, how I have worked around this in the past is to set up a MIDI trigger in this dialogue and create a User Actor that receives OSC, and sends MIDI (to a MIDI loopback).
Of course, you need to add the User Actor to every scene (or a constant background scene).
I'll make sure we have, adding OSC to the Go triggers Dialog, in the feature requests!