You have to get a voucher from them, and you have to at least buy your park tickets from them to get it. Occasionally they make you book your entire package to get them, but I think that depends on the location. I've gotten tix at two different
AAA locations and gotten parking passes each time. It was nice because I had an AP and the voucher was good all year (not free parking, just to get into the lot). But overall the parking isn't that great except maybe Epcot and AK. MK it's way too far and MGM is ok if they aren't doing construction in that part of the lot.