I still think new filters for the mono would be better
At the end of the day, even OIII has to pass through the RGGB matrix on the OSC camera so you're getting about 1/4 the data, limiting your resolution. You've got a mono already, I would (personally) just shoot with that.
That said, if you want to do it, sure, it'll work but in my mind, you're mixing 98 Octane with 95... just stick to 98
Might save you time as well if you can shoot both concurrently (but you'll need more exposure time on the OSC sooo.....)