They have a shuttle van that will pick you up at your resort and take you to GET your car. However when you return your car you are on your own for transportation.
Now, with that said. We tried this on Sat. Jan. 17th and had no luck at all! We tried calling and calling to get the shuttle to pick up DH and they kept hanging up on him! He would call back and they would seem baffled at how that happened but it did 3 times! So DH gave up and took the bus to MGM, then the boat to dolphin. It takes about an hour to do this. As this is how he picked up and returned the car and both times was about an hour.
Maybe you will have better luck with the shuttle van. We stayed at Pop Century and saw the van several times that week at the hotel. Of course if it stops at several hotels before taking you to the dolphin then you may be better off to go the other route.