Really good questions. Thanks for sharing. A couple of thoughts:
I absolutely think there’s less urgency for candidates if they are already employed. (And I will point out that both of the people who did this in our process were what you’d consider “passive candidates” and already had jobs. So that’s certainly a factor.)
You can learn a lot about a candidate by the questions they ask. If you describe the job the same way with every person, then say, “What questions do you have so far?” you’ll get a fascinating look at how people process information, whether they listen in real time, how deep they go, or whether they are just curious about the money or what the work hours will be. I think this is a big component that can serve both purposes. I also sometimes walk a candidate through an office and ask, “What observations do you have?” just to hear how they process it externally. I think this is another way to do both things as once. There are probably many more.