I've never heard of seeding the students with plants to ask verboten questions. Maybe my discipline is all fuzzy wuzzy and likes the rules.
The incident I remember was pretty blatant in retrospect. I wasn't really aware of the "forbidden questions" at the time, but I was present when an older faculty member told his undergrad research student to attend the undergrad meeting with the candidate and "see if you can find out if she is counting on us to find a job for her husband too". I hope this was not the norm, but I was startled when at a lunch with students during my own job interview a number of years later, a student asked me if I was married and if my husband was a ***ologist too!
OP- you have been given good advice - be yourself, but keep your guard up and keep in mind everything will eventually get back to the search committee.
While on the other end, our graduate students are told which questions are verboten, and strictly told not to ask them. Hopefully my department is more the norm than the other kind... (although I, personally, am pretty much unable to hide anything from anybody, even if its to my advantage, and will undoubtably tell people about my spouse & child even if they don't ask :-) )
