My experience is that aluminum holds paint at least as well as brass. If the aluminumis already factorynpainted, just lightly sand the lettering and other areas where thepaint is raised with 600 wet sandpaper, then paint away.
Don't forget - airplanes are mostly aluminum, and paint is not flaking off of them all that much. I just shoot extruded passenger cars with Scale Coat. Sticks fine.