I think the type of no work elsewhere contracts we get here in Canada, even for professionals, refer only to work in the same industry. For instance, if I want to tutor any students from my school, I have to either go through the school's own tutoring program (and make less money per hour since they take a cut) or get special permission. I even remember getting babysitting work from one of the families during the summer when school wasn't in session and having to clear it with the principal first!
With that said, I don't think the principal of my school would care if I spent the weekend writing romance novels or something, unless I was doing work for it during school time or on school machines. I mean, we even have politicians here who work in government but who own property or have family businesses from their prior career or something. Our mayor made much of his fortune on a family-owned furniture store. As long as he does not act in a way as mayor that gives his family business preferential treatment (there are rules for this and they are enforced by a watchdog) he can do what he wants.