For those who want to find this out whilst playing the game. It made me really disappointed when I find out.
Spoiler
Alduin and Akatosh ARE NOT the same. It says so in ingame books and Alduin refers to himself as "firstborn of Akatosh". Mightiest of the dragons(which are Akatosh's children. But not equal to/the same being as Akatosh.
Spoiler
http://www.imperial-library.info/content/shor-son-shor-full, maybe?
Most of the books on the subject are biased... and the Nords used to worship Nine animal gods.