I have to respectfully disagree that free range chickens don't receive much benefit from fermented feed. I'm sure your chickens do fine without it, and free range is certainly the most natural environment for chickens, so they're no doubt happier than confined birds, and a happy chicken tends to be a healthier chicken. But there are still many benefits to fermenting feed, including eating less of it (thus saving you money on chicken feed, which is significant to me since I buy organic feed) because the fermentation process makes the nutrients more available.
My chickens are quite free range also - several acres of both wooded and open areas, where they are allowed to be chickens. Fermenting their feed offers many health benefits, not just reduced incidence of coccidiosis, salmonella, E. coli, and campylobacter compared to chickens on dry feed (as shown by scientific studies). It also makes their poop less smelly and firmer, which indicates to me that this is what their gut has evolved to metabolize. Thus I don't see it as intervention, except in the sense that providing any food instead of allowing them to forage for everything they eat is intervention; rather, I see it as providing supplemental food in the form they most likely found it as jungle fowl before we domesticated them.
There are even more health benefits to fermented feeds than these, especially for very young chicks. The article I linked above does a much better job than I can at explaining them, and the author gives links to all her sources, so you can read the originals if you like.