The arena tours are difficult because of the size of the venue, but I've had a few hugs and hi-fives from pro dancers in the past when I've had front row seats - it's fairly easy to interact with the pros and celebs as they're leaving the arena if you've got dancefloor seats.
I've never tried to go to the stage door after a tour show but I've seen pictures of people having success meeting pros and celebs before/after shows so it must be possible.
I've met many of the pro dancers in the past (especially when some of the pros did their own tour at smaller venues) and they've almost always been very gracious and happy to sign autographs and pose for photos if asked politely