I have a bulk tape eraser left over from the days of reel-to-reel audio tapes. I have tried to erase DV tapes with this, and it has required many passes to even cause a slight problem with the tapes. Due to the high coercivity of the DV tapes, it is hard for me to believe that X-Ray equipment would be able to erase them--in fact, if they created enough of a magnetic field to do it, other metalic objects passing through would be drawn to the sides of the machine!
That said, I have been on 6 trips (12 passes through the machines) with DV tapes, and have never had a problem.