yep, the trip there took most of a day from aonang and is preorganised as part of the booking - its an all inclusive affair. Anything involving leaving ao-nang was exciting!
Don't recall seeing any scuba opportunities on lao liang, but if you are super psyched for diving I would absolutely recommend taking the ferry further (about 3-4hrs?) onto Koh Lipe - AMAZING! Here there is scuba/snorkel heaven on your doorstep (we stayed at place called "castaway" which had an awesome scuba/freediving crew annexed and loved it - best part of our trip....)