No, the radiation wavefront of soft X-rays advances in front of the visible light (it is what vaporizes the tower guy wires creating the “spikes” in some of these photos). It would destroy the fiber cable before the visible light was transmitted. Radiation also darkens fibers, which leads to it being of limited use in long term radiation environments. Also atmospheric tests were ended well before practical fibers were developed.
Can’t argue with that, however if the fiber reads detonation of the high explosive, there will be negligable x-ray production at that time.