In a recent seminar I heard an adult endocrinologist say that even though you can alter treatment in adult males who present with testicular rest tissue, the sperm cells may have been squashed and the CAH male may have residual fertility problems. 

However if I were you, I would put my ’eggs in the basket’ of trying diligently to stay on the prescribed dose of corticosteroids, for a good length of time, before I came to that conclusion!