No, of course you wouldn't hire a nanny who doesn't spank if you require them to spank your child under certain circumstances. You're talking about dealbreakers, and that is something that should be brought up as early as possible in the interview process. For both nannies and knowledge/technical workers.

Seems like a very interesting example to choose. Hiring a nanny for your child is one of those cases where you would absolutely want to fully vet each candidate. Are you suggesting you'd sooner leave the nanny's ethical and moral compass as a question mark than fully investigate what his or her ethics and morals are? This seems like a case where someone's ethics and morals are absolutely required to be known, not left as an exercise. Of course, most people rely on friends and family for such jobs for precisely these reasons. And if I had to hire a stranger, I'd absolutely be interested in knowing about their ethics and morals. Given my limited ability to get to know every last person, I'd prefer to hire from a reputable agency (so much as you can trust their reputation, in any case).

The reality of course is that every candidate will follow your orders up until he or she feels they violate his or her ethics/morals. Whether they're open about it or not is irrelevant. If you ordered them to abuse your own children (of course you wouldn't, but we're both being good-heartedly facetious here) you could reasonably expect them to turn you in, whether they were up front about it during an interview or not. Playing coy about the matter during an interview is a recipe for disaster on both ends.