I sat onstage for the Boston leg of the tour and you can kind of see backstage when you walk to your seat.
As for actually getting a tour backstage, unless you know someone in the cast, it is not likely to happen; however, I have heard stories of people with no connection to the show getting random backstage tours (I think I heard this with Wedding Singer). Anyways, you either have to be in the right place at the right time or know someone.
"We like to snark around here. Sometimes we actually talk about theater...but we try not to let that get in our way." - dramamama611