Yes you can. We did this last year. Quite nice, though very pricey. We also had a picnic setup for us on the private Atlantis beach.
I got the feeling there were many people there that day who were not guest of the hotel itself.
P.S.
The ride over the time we went was very scarey. Our boat almost capsized as the ferry hit one of the concrete columns of the large bridge that spanned the bay. No one had on life jackets, and my son cannot swim and he was only 4. People were panicking and I managed to grab a life jacket for my son, stuck it on his head tied it far faster than I ever though possible. The boat was damaged and a few people got hurt but once the boat stabilized in the water the boat limped to the nearest pier and we got off. The ferry operators dont give a dime about your life, and they are more than willing to push the boat to both it load and speed limit without any regard to safety. Please be careful.