I'm not sure I'm understanding your point. Can you elaborate?

From a prospective employer’s perspective: Is the candidate going to respect the NDA you’re planning to ask them to sign?

Similar to asking the candidate what they dislike about their previous boss. Their response may indicate how they’ll talk about you someday.

Oh, right. Yes I agree. We don't get employees to sign NDAs, but the signal about talking about previous employers is definitely something I notice.

So yes, if you get employees yo sign an NDA then this is a filter as well.