In addition to the "war graves" sensitivities, Pearl Harbor is still an active naval base and thus off-limits to civilians in general. And with the current world situation, the Navy, like the other branches of the military, is a bit nervous about security.
When I visited there in late March, Al-Queda had just set off bombs in Spain as a lesson for joining us in Iraq. I saw this nervousness on my tour of the USS Missouri, which is docked at Ford Island next to the Arizona. While taking the shuttle bus from the Arizona Memorial parking lot to the Missouri, the bus driver warned us that the Navy was prohibiting anybody from taking pictures as we crossed the Admiral Clarey Bridge which connects Ford Island to Nimitz Hwy. She even had recent stories of MP's confiscating the cameras of those tourists who got caught doing so, and urged us to keep our cameras tucked away in bags or pockets until we got to the Missouri just to be on the safe side.
While I don't think the bridge itself is so top secret (you can easily and legally take pictures of it from the Arizona Visitor Center or especially the USS Bowfin which is docked next to it), I figure there's something nearby, that's only visible while on the bridge itself, that the Navy doesn't want people taking photos of.
If the Navy is that sensitive about letting you take photos from a certain bridge, I seriously doubt they'll let you dive in their harbor.
