The volunteer process is a bit lengthy, but bearable. (I should be starting soon in a non-diving position). The requirements of DM or Instructor was, to the best of my knowledge, started because the powers that be at the aquarium seam to not want the liability. I was told that at first they didn't want a volunteer dive program, but later the guy in charge of diving basically said that it would be prohibitively expensive to have only staff divers clean all the tanks. For those reading that have not been to the aquarium, there is an emphasis on large tanks, which reduces the ability to clean them while staying dry. Also the big open ocean tank has sky lights, which causes algae to grow more rapidly than in the typical large aquarium with artificial lighting. In comparison the Tennessee Aquarium, where the guy in charge of diving worked before, there were something like 130 volunteer divers (don't quote me I don't recall the number exactly.) and the GA Aquarium is much lager, so there should be a considerable program as they get rolling. BTW, most of the diving is surface supplied air.
For those who haven't attended, a word of caution... I had a hard time visiting, because of many days afterwards all I wanted to do was go diving... to stand under the tunnel and have a huge school of fish swim overhead made me want to go diving so bad...