It's pretty unlikely Olaf has mites. Gliders are very proficient groomers, which is probably what he is doing. It can look like scratching, but he is just combing and cleaning his fur.
Gliders do this "sneeze" thing in their hands and feet to clean themselves, and or lick their back foot.
They have two nails on their back feet that are longer and skinnier than the other two nails on the same foot, the skinny nails are their grooming nails and they do NOT need to be trimmed.