has anyone ever added or at least removed the overhead panasonic dvd unit?are all escalades able to accept these units even if not installed from the factory?

Depends. Does the dvd you are getting come out of a car that had a sunroof? Does yours have a sunroof? You will most likely have to run power to the unit. My suggestion is to run power from the ignition switch so the unit only powers up when the vehicle is on like any other accessory type of item. If youre not sure, hit a reputable aftermarket stereo shop, they can make it work.
If you have not purchased it yet, see what they are offering you may be surprised.