I placed a lightning rod at an altitude of about Y:20 on a superflat world, connected to a tower of glass blocks to transmit the redstone signal downwards.  On starting a thunderstorm, the lighting rod was struck within minutes.

I extended the redstone tower upwards to Y:>128, with repeaters to boost the redstone signal.  Testing with a lever resulted in the tower operating as expected, but when I replaced the lever with an upward-facing lighting rod (as in the successful test), the lighting rod was not struck by lightning even after an hour.

Reducing the tower to Y: between 100 and 127 also failed to result in lightning striking the rod.