If you do the bare minimum work as a tenured professor you're going to get an awful lot of people extremely mad at you at all levels of the academic hierarchy.
If you do the bare minimum work and you're spending a lot of time on your own company, at my university, you will almost certainly get a pink slip. Doesn't matter if you have tenure. We are not allowed to work more than one day a week on such things, and that requires approval, which probably won't happen if we're not publishing, have terrible teaching evaluations, and aren't doing a full share of service and advising.