Let your birds decide. They're alot smarter than most give them credit for. I thought it was weird the first time I saw one eating a feather till I learned why. No, maggots are not a parasite, look in the Webster for reassurance.
Absolutely! Maggots are nothing more than fly larvae and chickens love em! I occasionally will go to the pet store and buy an container of meal worms as a special treat but learned early not to feed by hand, they tore me up trying to get to them!