I've seen plenty of HPS & Metal Halide floods & wallpacks that were supplied by 208 volt or 240 branch circuits and were individually controlled by a photocell. Since these fixtures came from the factory that way and are UL listed, I think the second paragraph of 90.7 would allow a factory installed photocell to switch just one energized conductor.

Of course, if you're the AHJ, it is up to you to approve equipment, listed or not.110.2

Few things are harder to put up with than the annoyance of a good example.