At the end of the day, there are no rules and YMMV. As a curiosity, I wonder how much time John Carmack spent coding as CTO of Oculus. Chances are there are very few people in the market with his coding talent, and if someone like him wants to code, you're going to make it work.
EDIT: yep, just as I suspected :D https://www.quora.com/What-will-John-Carmacks-role-be-at-Ocu...