Sometimes chickens get sick and then get better all on their own, sometimes chickens get sick and people feed them herbal formulations and they get better. This does not provide any proof that it works, nor any that it does not. Some products/suppliments may well have a profilactic effect just as would any good balanced diet. Apple cider vinigar for example likely helps by controling crud and bacterial levels in the waterers as well as acidify the digestive system sligtly. Which should help the birds fight off yeast type infections and thereby give a helping hand through healthy digestion in fighting off things like cocci or worms. Still apple cider vinigar is in its self not a cure for either.
There are antibiotics that have been proven effective on many respritory infections, feeding them is a personal choice. I have not needed too in a long time knock on wood and like to keep it that way, but if need be I would rather treat agressivly at the first signs of real trouble to minnimize the spread.
One very first natural step if there are any signs of respritory troubles is make certain the coop is clean, dry and well vented, high amonia levels can cause respritory symptoms and certainly stress the birds leaving the birds leaving them open to infections.