Yes, I just got the DDP and made my reservations for various meals, including the Fantasmic package the night we're at MGM. However, you still have to secure the reservation with a credit card, $10 cancellation fee/person if you don't show - even if you're paying with the DDP. You have to cancel 36 hours before the reservaiton or get the charge.
Also, even if there is availability at the restaurant you want, it doesn't mean you can eat there with the Fantasmic package for the same availability. I wanted Mamma's and they must have filled their quota of Fantasmic packages, even though I could eat there that night sans package. So I went with Hollywood and Vine.