The three pins were intended to connect a MIDI port if the BLM wasn't used, hence using the standard MIDI pins and leaving the others floating. This was before the days of MIDIO/MIDI8. So it should work to connect, but yull deffo need some bodge wirez maaate!
Keep in mind that the SRIO signal can get dicey if the cables are long. This would be the idea of the Line Drivers.