On the first point, I don't know. Sorghum is a seed often used for pasture in game plots. I doubt there is a difference whether it is just sprouted or growing in the ground. I could be wrong.
On the second point. You are absolutely correct. There is no grain one can feed, ferment or sprout that will provide all the nutrients chickens are known to need.
As omnivores, chickens have always eaten all types of bugs as well as frogs, mice, etc.. This is the animal protein that omnivores need. Animal protein contains all the essential amino acids needed in the diet. Vegetable protein will always be incomplete in essential amino acids. Many manufacturers make vegetable based feed, they can do so by adding synthetic amino acids like lysine, methionine and sometimes threonine and tryptophan. Whatever is missing in the grains/legumes they're using as the base for the feed.
