I heard same, but I have NO confirmation.
My default re: casino cheating is that if it refers to an Indian Casino there is a good chance that it is true; but if it isn't a tribal enterprise, it is doubtful in most cases.
Incidentally, casinos that deal H17 games will cheat you more effectively by adding FOURS (4's) , not FIVES (5's); because that not only falsely inflates the True Count, but it aids their dealers in converting SOFT 17's into 21's.