For a pile, probably.Regarding sheet or pile composting - I think you'd want to cover the manure with a carbon of some sort (dried leaves, wood chips) to keep flies away.
For thin layers, it would depend on the climate.
In hot, dry weather it might dry so fast the flies are not interested.
In really rainy weather, it might wash into the soil so fast the flies are not interested.
In below-freezing winter weather, there will be no flies until it thaws in the spring.
For weather that is not any of those extremes, I agree that flies could be an issue even with layers spread thinly on the ground, unless they are covered with something.