Starting the video isn't the problem, stopping is - killing the videoplayer needs root.
I haven't found a different way to tell the videoplayer to go away when the door closes and the sensor triggers. Might start a different app, hoping that the videoplayer realizes that it's not visible anymore, and stops the video. I guess it'll go into pause mode, though, which wouldn't help.
Root or no root, what physical methods do you plan to use to protect the tablet from people trying to tamper with it? Root access can be passcode protected, using the proper SU app :-)