When I last did ACL, the ALD called the spot cues due to the large number of both light and spot cues. This was also a summer stock setting: 15 hours of tech, 8 performances. And for the good of the show it was much better to have one person focused on talking the spots through the show. There were certain moments when I would open the headset channel to the spots to help make something clean - i.e. the spot bounce down the line at the near the top of the show. Ironically in the end, I could have called both as when spots were heavy, lights were not and visa versa, but I did not have time during tech to verbally "teach" the cues to the ops as well as calling the other cues.
I do wonder however about the light board op calling the spot cues, simply because they should be focused on when you are saying "GO" for the board cues. And what if something goes wrong on the board? It seems to me if they have time to call the spot cues, you must have time to call the spot cues. I would agree with kiwitechgirl, if there is a specific spot caller, great, but I would be nervous about the board op doing it.