AP holders can buy the
DDP without having to buy a park ticket
only if they are paying rack rate for the room or if they are using an AP discount for the room. If you are using a PIN code, a GP code, Bounceback deal, or
free dining, then you must buy at least a one day park ticket (two day park ticket for free dining this year) just like anyone else.
For example last fall I booked a room at rack rate for May 1st-9th. I told the CM I had an AP and so was able to add the DDP without buying a park ticket. When I was at WDW in Dec I switched that reservation to the 35% off bounceback deal. The CM mentioned that with the Bounceback deals I'd have to buy at least a one day ticket for everyone in the room, even though I had an AP. I knew that but even buying one day tickets the ressie was cheaper, so I did so. About a week after we got back, AP discounts came out and so I called and switched the ressie to that. It saved me an extra 5% on the room and plus I was able to cancel the one day park tickets I didn't need and was still able to keep the DDP.
I currently have two more bounceback 35% off deals booked for Oct and Dec. For those deals to add the DDP, I had to buy one day park tickets (even though I have an AP). However, when/if AP discounts come out for those dates then I'll be calling to switch to that discount and so will be able to cancel those one day park tickets. If AP discounts don't come out, then I'll be stuck having to buy one day park tickets because they are required for the bounceback deals or any GP deals that may come out.
Last spring I booked the buy 4 get 3 free deal, but even though I had an AP I still had to buy a one day ticket in order to add the DDP because that deal required them. The same thing happened for our trip last Dec. I originally booked under a % off PIN, then switched to a GP offer, then to an AP discount, then finally to free dining. A one day park ticket was required for every deal, except the AP discount. Again the only way to get out of buying one day park tickets is with a rack rate room or a room booked under an AP discount. Any other room discount is going to require a one day ticket in order to add the DDP.
Just FYI: you can not just add the DDP to a room only ressie. When an AP holder adds the DDP to a room it becomes a ticketless pkg with all the pkg rules attached to it (must be paid in full by 45 days out and penalties for canceling less than 45 days out, etc).