It undoubtedly helps. There're plenty of counterexamples though: Steve & Steve from Apple, for one. And I don't think it's more that they have a higher chance of starting a business, it's more that they have a higher chance of finding the money and time to succeed with their new business.

Also - the elephant in the room is plain old intelligence. Ivy League colleges tend to admit smart people, at least as closely as they can determine (there're always a few doofuses who sneak in, but they are a smaller proportion than at community colleges). Smart people have a higher chance of trying to start their own business, and a higher chance of being successful once they've tried.