yes, it will oxidize aluminum, but that oxide layer is good... it just looks ugly.
i've used oxiclean for many kegs when i first get them (all used), and it works quite well to clean them up.
Walk-In Serving(14): Flanders red, Hard Cider, Belgian Tripel, Liquid Stupid, Wee Heavy, American Brown, Rye IPA, American Amber, Imperial Stout, Dry Stout, Cream Ale, Belgian Wit, Traditional Mead, Oatmeal Stout
Walk-In Cold Storage(~50): lots of beers, meads, and ciders
Oak Barrel: Flanders Solera