I think you are looking at the wrong end of the
system. I've spent a few years maintaining electronic equipment attached to radio towers, which are basically giant lightning rods. Generally, the components closest to long cables wind up acting as fuses protecting everything else.
Anything is possible, but I would be very surprised if lightning damaged the
DMX cabling. It is much more likely to damage electronic components first. I would concentrate on the
DMX receiver components in the
DIMMER rack. It obviously still functions to a limited degree, but a termination
resistor, a pair of
shunt resistors, or the chip may be fried enough to change the load to a value way off from the standard 120 ohms. Or, it could be half dead, making it un-balanced. That would make it hard for most devices to drive the input.
A possible reason that the USB device works is that it just happens to handle a mismatched or unbalanced load better than the consoles.
The nice thing about lightning damage is that it often leaves physical signs of damage, such as discolored components, burned traces, soot trails. If David can tell you where on the
dimmer control board to look for the
DMX input, you might be able to see what's wrong.
I do hope
ETC has the good sense to
socket that input chip, and to not use surface mount components in the section vulnerable to outside influences.
If you still have reason to suspect building wiring,
disconnect the cabling and connect a short
DMX cable directly to the
dimmer rack, then test the consoles. That'll eliminate a lot of variables
in one step.