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.

This is precisely correct. And even if I could get away with it, I would not feel that it is morally right (for me at least).