Without a doubt! Ao Nang is a very beautiful and scenic area. The limestone rocks are very unique for this province of Thailand. If you are a bit into rock climbing - Ao Nang/Railey Beach is your destination.
A short distance away from Ao Nang, you'll have several small islands, which most dive centers in Ao Nang using. Koh See, Koh Haa and Koh Yawasam are very popular and recently some new wrecks have been added to create some artificial reefs. While the visibility most days are not fantastic, the diving is better than most dive sites around Racha Yai and locally on Phuket.
Phuket and Ao Nang sharing only Phi Phi islands, Shark Point, Anemone Reef and the King Cruiser Wreck. Specific for Ao Nang is daytrips to the local islands, Koh Haa and speedboats to Hin Daeng/Hin Muang. Special for Phuket are the Racha islands as well as Similan islands. This is scheduled trips and nothing about what can be arranged.
Are you saying the diving is not that good around Racha Yai and when you say locally on Phuket, what dive sites are you referring to?