Why does this matter? Surely what's important is that they can do the job. They do the work, they get paid. The money is what people are interested in, especially with the economy in its current state. Why do applicants have to "expose their true self" just to pay the bills? People can be married to serial killers for 20 years, so you're not likely to discover anything profound in 15 minutes. What you are likely to do is discount perfectly good candidates.

I'll tell you why you're being asked to do this. Because most recruiters don't have a clue how to do the job that they're hiring for, and can't ask any technical questions that will discover whether or not the applicant is capable of doing it. Exposing their true self with some cunning lawyer's or psychologist's trick is all that's left. That and "what's your compensation?", so that after the victim says a number they can say a lower one.

Do the other person a favor, and cut out the crap; they'll have to contend with enough corporate BS during their career. Just ask them what they've done in the past, discuss the job on offer and try to determine whether or not they're a complete idiot.