After recently defeating the DLC 'Mad Moxxi's Underdome Riot', I was saddened to find that all I had received were a handful of trophy achievements and a Badass Skill for each area conquered. However, when you go to store items in the bank you can see a wall filled with little cash boxes, and if you look close enough, you can see at least three weapons chest in an open vault door. Can these be accessed or are they just for show?
I believe they're just for show; I don't think you can get past the bars.
(Of course, now that I'm posting this, someone will post a YouTube video showing them waltz into the vault.)