I have done the Dine with an Imagineer program twice now. While neither was one of the big names you hear most about, both of them I have seen on TV on the Travel Channel. One was definitely an exec level person.
You definitely have the chance to ask a lot of questions, but the imagineers really like to talk abut what they do as much as you like to ask them questions. Both programs I was in lasted a good couple of hours, and you spend more time talking with the people at the table before and after. The group is nice and small and informal, so it's definitely NOT canned! They are NOT on the defensive, believe me!
Have some questions in mind to ask, but you will think of more while talking. One impression I picked up during the meal is that Imagineering is a lot more vast than you think it is, and no one knows all the details of every job or project. In fact, what I found most interesting is learning more about how they work. You tend to think of imagineering as one small group of designers who just come up with ideas, and after this you realized how many different aspects there are, from meeting with the marketing people to design development, to all the construction.
I would most certainly recommend it to anyone, and it is worth the admission price to the park alone for it. Like I said, this is my second time in two years, and I am debating whether to try again a third time. I found it quite interesting and a totally new viewpoint on the Disney Magic.