Hi @veganpete,
It is definitely possible: Sonic Pi can receive and send both MIDI and OSC messages.
(See http://sonic-pi.net/tutorial#section-11 and http://sonic-pi.net/tutorial#section-12 if you haven’t already).
I have never used this feature myself (so someone else will no doubt have more knowledge about it) but here is a possibly relevant example: Polyphonic gated synth for Sonic Pi 3, works on a Pi3