I have asked that question since 2006 for my first trip, and I just got back from my 2nd trip. There answer to me was no, they are not allowed... But you know security doesn't look at the whole cooler, just turn the wheels to you and they can easily over see it. I saw them in my first and 2nd trip, and I was always thinking to msyelf, I should of brought it, I should of brought it. So i'd say, try it. I've seen them there. They are so helpful... But the rule is no...
Have fun...