Can annual pass holders purchase the dining plan if they are staying at a DVC resort - or must you purchase the dining plan in conjunction with Magic Your Way tickets?
If you are staying on DVC points, you can purchase the DDP without purchasing a package/tickets. However, all the different plans are not available - just a few. (not the premium or platinum)
If you are talking about purchasing the Dining Plan, any DVC member (or guest through a DVC member) staying at a DVC resort can do so; that has nothing to do with the park tickets you purchase.
If you are talking about the free dining plan, you need to purchase a Disney reservation and ticket package through Disney because it is unavailabe to DVC mebers or to AP holders.
Are you paying cash for the reservation, or using points?
On cash reservations, you can book a ticketless room/dining package for AP holders, even if your cash reservation is at a DVC resort.
If you are staying on points, the type of ticket you have is not relevant, you can always add DDP (or if you're renting, have the member you are renting from do it) without a required ticket purchase.