Pretty much everything does. The question is how fast. When steel rusts, it manages to increase the surface area available to more chemical reactions, which is why rust spreads like a cancer. I don't think aluminum does this.
Under normal conditions, aluminum oxide forms a protective layer for the rest of the aluminum. This goes out the window for unusual sorts of corrosion (say, mercury).
Really? Someone should really tell the manufacturers of boats then.
If your boat is only aluminium you don't really need the anode. it is only when in contact with other metals that aluminium has serious problems in sea water, as it becomes the sacrificial anode to your steel or brass, so you need zinc then as it has an even lower potential.