The response of the photoelectric smoke detectors would depend on the concentration of smoke in the cargo hold. This, in turn, would depend on the air circulation through the cargo area.
The design of the fire suppression system is to bring the compartment halon concentration to an initial 5% and maintain it at 3% for the time needed to divert (60 min/180 min for ETOPS). So the need to maintain a minimum halon concentration would contraindicate any ventilation that would clear smoke and the detectors' alarm condition.
Depending on the naturer of the smoke, it might hang around for some time (along with the alarm condition) after the fire was extinguished. If the smoke source was initially localised, it may dispurse on its own throughout the hold and drop below the detector threshold more rapidly.