I personally know Niel Amrstrong and Gene Cernan... I won't speak for Neil he is a man of Huge integrity, so if he was told to keep a secret I think he would. As for Gene, who has been to the moon and back twice, and walked there once... I think if there was something to hide he would have spilled the beans by now. He is a true space cowboy.
That being said I have NO doubt both these men walked on the moon.