My dad had a CABG x 5 three years ago, he's a type II diabetic. He did great. I think if you talk to your dad's surgeon, you'll find it's pretty common for type II diabetic patients to have bypass, and they see a lot.
It's typical after any heart surgery to get insulin, so you should expect that, even if he doesn't usually need it. I found that my dad ate marginally better after his surgery and he's since been able to come off meds, they were dropping him to low. With a diagnosed heart condition, you'll want to keep a close eye that his sugars don't start dipping to low, that's bad for the heart.
Best of luck!