Are the aluminum ladders rust proof?

The aluminum on the ladders is rust proof. However, there are some parts that may rust over time, depending on the environment. Some of these parts include rivets, nuts and bolts that attach the locks and shoes, and the spur plate on the shoes.

theoretically it shouldn't rust, but it can...especially the welds, which manufacturers typically 'coat', but you could always buy some paint to protect (and pertify) whenever some rust shows.

Aluminum does not rust, it corrodes, but at a very very slow rate, if you look at an old aluminum boat for instance, you will notice a grayish spotting on the surface, this is the oxidation effect on the material. Aluminum can last for decades and the corrosion is typically only on the surface, there for retaining the strength of the metal for years.