That may be true where you are, but in Atlanta there is a sizeable Hispanic immigrant population in the churches. Most parishes offer one or two Spanish masses each week. I don't know whether they are officially registered or not, but they are certainly attending mass in large numbers. When we moved here 12 years ago, our real estate agent told us that "there are lots of religions here, even some of those Catholic people have moved in". Now there are 8 parishes within 15 miles of here, seating 1000+ at 6 or 8 masses per week.
If you compare the number of Hispanics attending the local Spanish Mass to the number of Hispanics living in the boundaries of the Parish, you'll see that most are not in Church, and its not even close.