I can't say who runs the concessions, but the snack bar is in the building that you have to go through to get to the camp. It houses the bookstore, restrooms and a little exhibit of people who worked for the Resistance. 

I am not saying/suggesting anything. I'm just saying they sold hot dogs, purchased in the lobby, maybe 100 feet from the infamous "work will set you free" sign.

Seemed a little weird is all, but I bought and ate one on the bus between the short ride from Auschwitz to Birkenau.