There's risking mold because of a tiny unlikely chance when stored well of a food needed in the diet and then there's a stupid risk because of an item that often grows mold even when harvested and stored correctly that is not needed in the diet. How often have you run in to moldy hay? We bale hay, buy hay, sell hay, and feed hay to rabbits, guinea pigs, chinchillas, and horses. I have seen moldy hay once. The guinea pigs pulled some down, peed on it, covered it in bedding, and then one ate it and died. Once in my entire lifespan of raising animals. There's also a very distinct smell to moldy hay and often visible mold. The high risk items include peanuts, corn, and grapes/raisins which have killed animals or made people severely ill with no warning even when stored correctly.
Yes there are healthy treats. Rosehips have no negatives and are often fed daily. Many dried flowers and herbs have no negatives and are fed several times a week to daily. Sure some are not safe for that often but many are. They provide a nice range of nutrients that could be missing from hay and the stuff in pellets is not stable forever. It's also healthier to get your nutrients from natural sources than from powdered vitamin/mineral supplements which is what pellets and vitamin pills are made of. Cereals can have sugar but if you pick out the right ones they may have no added sugar or less sugar than your pellets and the same grains as your top pellet ingredients so they are barely any different than feeding pellets. In fact we are experimenting and researching making a supplement out of grains, herbs, dried flowers, and oil seeds (flax, chia, sunflower) to feed a small amount nightly to each cage. Basing it on existing supplement mixtures, suggestions for what can be fed how often, and research done in to wild chin diets.
I don't feed any of my other animals on commercial food. I took several animal nutrition classes in college and then did my own research in to individual needs. The only thing we have on a commercial pellet is the chins. All rabbits, dogs, cats, hedgehogs, horses, gerbils... are fed on a species appropriate diet of fresh ingredients.