I don't know if aluminum has the same concern, but there is a story in Diver Down about a guy who used a steel tank that had been filled and then sat for a while. He died. The air in the tank had a bit of moisture in it. Over time, that allowed the inside of the tank to oxidize (i.e. rust), which uses the oxygen in the air. He was only doing a very shallow lake dive. When they analyzed his tank afterwards, I think the book said they found it to only have something like 5% oxygen.
I don't think aluminum oxidizes the same way steel does, so it's probably not nearly such a concern as if it was a steel tank. But, I would still at least use a regular O2 analyzer on it, to make sure it's breathable.