I have tried for a while now, and I thought I could do both. But... (1) It is difficult on a personal level--for example last month SageMathCloud got hit by a major DDOS attack 15 minutes before I had to teach a class. I have family and though I love to work, there are only so many hours in a day. (2) There I am at a big old state university, and there are many complicated byzantine conflict of interest and IP rules, which have been a pain to navigate, and our university commercialization office isn't the best. (3) Investors greatly prefer that the person/company they are investing in is not just a side project for the person running it. All that said, the mathematics department at University of Washington is full of supportive faculty; I'm doing what I'm doing more for the people I want to hire than just for myself.

But you can't be a professor and work full-time on another project, which is what he wants to do.