I would not place any live rock from anyone into my tank w/o curing it first no matter how cured the store claims the rock to be, you will not kill the benificial bacteria by curing the rock, in fact the more stuff the rock has that dies off in the curing process will elevate the bacteria colonies need it to become your natural filter.
There may be bacteria that needs light for survival but the one that the live rock uses for filtartion lives deep inside the rock and i am pretty sure will not be affected by darkness, the reason behind curing in the dark is to kill any algae, the amonia spike that the die off will cause will take care of most of the other critters, the lack of food will take care of the rest, 3 weeks to 1.5 month is a good time to cure the rock.