I know its not in halo 2 but, It has 2 points. 1. I hoping to build a prop armory and it was the first one i chose to do luck of the draw first plans i found and so on.
2. Its in halo 3 and Halo 3 odst. so lore wise even if its not in the 2 you can assume those arms were not allocated to that area. I know it a stretch but that's my excuse lol