Tommy,
Core aeration and using a Hydroject are two different methods. Core aeration is for physical removal of organic matter and incorporation of fresh sand into the core holes to assist with percolation, root health, thatch, compaction and the like. Units like the Hydroject only create small channels into the profile for increased oxygen and gas exchange. They do provide benefits to roots as well but don't assist in physical removal of organic matter. Hydrojects were ahead of their time and are hard to find today. Newer units like Air2G2 utilise similar principles to the Hydroject but shoot compressed air into the profile rather than water.