The Octatrack can send out a MIDI clock signal from its MIDI out that you could route into the input of the Prophet 12. So, by setting the tempo on the Octatrack, it could affect anything on the Prophet 12 that can accept a MIDI clock, like a LFO.
You can also use the Octatrack to sequence notes on your Prophet 12.
They would make a good hardware-only team I think!