I purchased 3/8 Brazilian Cherry (solid). My installer says the existing sub floor is not suitable for a good installation and wants to put a 3/8 sub floor over the 3/4. He wants to glue the hardwood floor instead of stapling because he's says it will be a better job. Does someone concur with this assessment? Just looking for a sanity check since I don't know the answer. Thanks.

Sounds as if he is looking out for you, instead of his own pocket.