Just to clarify a little since you seem to be new at this...bluetooth sync really is just the general format of connecting the device to the car stereo, it really isn't specific to any one app, so you can pretty much use any app you want to play music and as long as the basic bluetooth connection is made to the car stereo, it'll play the music through the speakers.
Something important to make sure of though before you head out with your rental (that we did not make sure of before we left on our Cali road trip last year with a rental Mustang convertible)...make sure you GET a radio in the car that has bluetooth connectivity. Ours only had a wired connection, and we were a little shocked (but it worked out ok anyways).