Oh yes. I have a very intimate relationship with grain mites, having accidentally sniffed some of the critters up my nose as I was looking at them through a magnifying lens.
Grain mites are in everything of a cereal nature - wheat bran, flour, pancake and cake mixes, and especially chicken feed. However, they usually do not come to life in a scary way unless the conditions are right. The temperature needs to be warm and the humidity high.
Even a major grain mite hatch in your bags of chicken crumbles shouldn't be a danger to your chickens unless the moist warm conditions have caused the feed to start growing mold. A good way to prevent grain mites is to keep the feed in a cool, dry space, bags secured shut against absorbing moisture from the air.
Use your nose to detect if the feed has absorbed so much moisture as to render it moldy and a health danger to your chickens. There's a very big difference between fresh feed and damp, moldy feed. The grain mites are an important clue that the feed could be going bad. I wouldn't worry about the grain mites so much as the quality of the feed.
