jmseiver:

Do you think that my older Roland FC-300 will work?

Yes.

Some find MIDI programming daunting.  Considering your degree, you'll be in BASIC or FORTRAN 101 territory with this.  I understand the time crunch, but we're talking about plugging in one CC value for key – and one CC value for scale – as a start.  Any other key/scale combinations are variations on that theme.

The first important steps are to dust off the FC-300, download the manuals & reference guides, and get the Roland and Eventide units to talk to each other.  Once you have that going, there's no limit as to how far you can take it.  But you can get exactly what you want – real time harmony changes – without having a complete understanding of all of MIDI's nuances.

Maybe make a visit to MIDI.org, or an online MIDI guide.  You don't have to learn it all right now.  Just how MIDI CC (continuous controllers) work, and how that applies to your Roland FC-300 and PitchFactor/H9 Diatonic algorithm.  Everything else can build on that foundation.

I usually carry the programming and reference guides around in a tablet for any new piece of gear.  When I get a spare second, I'll try to 'configure' that unit in with my existing setup.  When I finally do get the time to sit down with it, there's no fumbling around with the basics.