Not sure if this "is done all the time" or not, but if I'm a coach and an AD goes behind the current coaches back to "gauge interest", I'd have to ask myself if I really want to uproot my family and relocate to work for someone who operates this way.
The flip side to that is what does it say about a coach who's willing to entertain contact and interest behind the scenes. Does that make him a long term solution? Does it speak to his character and commitment to his employer? Might be a totally different world in college business, but those are thoughts that would run through my mind.