The bus is not shared with anyone... I think it's the best bus service on property! I have never waited more than 25 minutes for an AKL bus. I have waited MUCH longer for buses at other resorts, and we had horridly long waits to get back to the hotel from the parks when we stayed at Pop Century... we would get back to the hotel about 2 hours after leaving the parks, it was just horrible, especially when the bus stop was the last one in the lineup at MK and the end of the line was almost back to park entrance! Last year we had a couple of late dinners at the Poly and the bus there really stunk too, they take a very long time to get there, then you have to go to other resorts and if the parks are already closed you end up going to DTD and then have to wait for another bus to get back... makes for a very, very long night.
In short... you should LOVE the bus service at AKL and I wouldn't even think about renting a car while staying there... Pop, yes... AKL, no.