“Doctor, doctor, it hurts when I do this.” 
Dorico in general should pick up MIDI devices when they appear, but the problem may well be that once the MIDI device appears as an output, it will also be chosen as an input, on the Play page of Preferences. If you have the same MIDI device chosen as an input and an output, you’ll end up with a MIDI feedback loop and that may indeed result in Dorico crashing.