Having a dedicated video card is preferred, but I think it will depend on what software you are going to run. If anything will run with onboard graphics I'm guessing it will be Visual Pinball.
To be honest, I didn't even try to run my setup without a video card, so I don't really know what performance will be like
I picked up a used GeForce GTX460 for my build. There are plenty of these under $100 (and that's probably overpriced). I have had no problem running Visual Pinball, Future Pinball or Pinball FX2.
Keep up the good work! Your cab looks amazing so far