Well, mine was listed on the factory sticker, but I've found no way of playing or controlling the headrest units through the head unit and I've got the factory NAV unit nor any way to play a dvd from the head unit to the rear headrests.
I found this in the NAV guide from my Expy.
REAR DVD SYSTEM (IF EQUIPPED)
Note: The images seen in this section, and the functions they represent,
are only available with the headrest DVD system and are only available
on Flex and MKT vehicles if the headrest DVD option is ordered
from the factory when ordering the vehicle. For all other headrest
DVD systems installed on vehicles other than the Flex and MKT, or for
headrest DVD systems installed on vehicles already available in a dealer
inventory, these functions are NOT available.
Your navigation system allows you to access the dual DVD headrest
system (if equipped). To access:
1. Press the MEDIA hard button on the navigation system.
Well if that isn't interesting. If it's on the sticker, you're supposed to be able to hit the MEDIA button and see the "Rear DVD A" and "Rear DVD B" selection buttons under the "Jukebox" item. In your case, I'd contact Ford and ask them about it.