Nope, I am not recommending bleach but I will explain why some companies do. Some of these same companies say don't use vinegar or baking soda. There is no good reason for this. I will explain all three things in this post.Also this post isn't putting down these companies or their products. They provide a good CD option. but like all diapers they have their pros amf their cons. Understanding the cons allows you to better care for these diapers so you can enjoy all the pros they offer. Also I would say these are quality companies. The instructions they give are to simply make sure the products they make will work for you and they have conveyed that advice in as simple and basic a format as possible by creating their own basic care instructions.
Why some companies recommend bleach: What is known as the modern cloth diaper are diapers with synthetic materials such as microfiber, suede cloth, minky, binky (bamboo minky), fleece etc. The construction and shape of the fiber is different then natural fibers. In fact when microfiber was designed (by the cleaning industry) it was designed this way on purpose to pick up and trap dirt, bacteria etc. At the end of this post are some pics from a microfiber industry site - check it out. Since its designed to trap these things, they are harder to wash out. The result is that these fabrics are more prone to ammonia (which some people refer to as stink), which makes your diapers smell bad and will cause a rash on babies bum, in bad cases it will cause ammonia burn. If your using a "modern diaper" which also has thick layers then your increasing the difficulty in washing the diaper because there are more layers to wash through. This is also why its important to remove inserts from pocket diapers. Washing inserts that have been seperated from the diaper allows you to wash through less layers resulting in a cleaner diaper. The solution is that some of these companies will suggest a monthly bleaching, to combat the problem. Am I saying people shouldn't use thick "modern" diapers? No. These diapers have qualities Moms like. And if for you their pros outweigh the cons then use them. Just be mindful of the drawbacks. Change the diaper even though the fabric leaves it feeling dry. Remove all poop before placing in your diaper pail or wet bag (should be done with all diapers). Rinse out overnight diapers (should be done with all overnight diapers). Wash often (again as with all diapers). And make sure you have a very thorough wash and rinse routine. It will need to be more intense then with flats, prefolds and basic fitted's made of natural materials. Keep a sharp eye on the diaper for signs of ammonia or build up. Extra detergent or water will not clean better. An extra washing, boosters (some if which are hard on fabrics), vinegar presoak or rinse should help. In the end you might need to follow the company advice of monthly bleachings. If this is the case absolutely do a vinegar rinse at the end of multiple post bleach rinses. And do not expect all these diapers to last forever. In the end the bleach and washings will cause wear, it just happens. If the only way to keep ammonia at bay is a monthly bleaching then that's because they could not be completely rid of ammonia. I would suggested not reselling or donating a diaper with this issue because it's just not right to be passing an ammonia problem on. In addition I recommend looking a cloth diaper blogs. Find one by an experienced CD mom. Experienced as in over a year, at least, multiple children is even better and doesn't have repeated ammonia or leak issues (which build up creates). And lastly one that uses the same or a similar diaper. A mom using the same or similar diaper and successfully keeps the diaper free of its potential issues will be a good resource. I can only advise so far. I understand fabric and sewing very well. I've always been good at science and research. And I've been cloth diapering longer then most but my hands on experience is keeping basic fitted's and prefolds made of cotton clean.
* If you are using a diaper made of natural fabrics but 8+ layers thick, you also will need a more thorough wash and rinse routine in order to wash through all the layers. This means you might need to follow much of the same advice.
Why white vinegar is safe:
White vinegar is also called distilled. Technically speaking, its not. What it is, is 5% to 8% acetic acid (that's vinegar) in water. With a pH of 2.2-3. This makes it too weak to breakdown fabric fibers. It will however breakdown detergent and uric acid. So what's their problem with it? Well it is possible that striping with vinegar might not be strong enough on synthetic fabrics to strip them. So what you could do instead is use white vinegar in a presoak before washing or add to the rinse cycle after washing. Do that with each wash to help hard to clean synthetics.
Why baking soda is safe: Baking soda (and washing soda) have been used in laundry and cleaning for over 100 years. They are safe and they are gentle. They do not have the ability to harm fabric (they are not strong enough to do so). They also clean nicely. Washing soda cleans better then baking soda however. And if all you have is baking soda you can bake it and it will turn into washing soda. So why do some companies say not to use them? Same issue as vinegar, these are safe gentle cleaning products which may not be strong enough to clean synthetic materials in a diaper.
The pics below come from a microfiber industry site. The top diagram shows why and how they do their job of picking up and trapping dirt and bacteria. The second picture is a photo of a cross section of the fiber under a microscope. It is also why they work as stay dry fabrics instead if absorbing fabrics. The fiber design does not allow the fiber to swell up with retained water.