I've used Neem Oil/soap on flowering plants. I haven't noticed any bad effects, although I try not to use it during the last 3 weeks. I understand that many growers who suffer from Powdery Mildew and other fungus use it regularly.
I wouldn't use a sulfur spray on buds, it might affect the taste. When I've used a sulfur vaporizer in the flowering room, I've always hosed off my plants really well before harvest.
HTH
