The statute I see referred to earlier in this thread refers to mandatory reporters being "school employees". And "school employees" is defined as "an individual who is employed by a school or who provides an activity or service sponsored by a school. The term does not apply to administrative personnel unless that person has direct contact with children."
In this case (assuming, of course, that the definition is correct) the only school employees who are exempt from being mandatory reporters are administrative personnel who do not have direct contact with children. Penn State, I believe, would qualify as a "school" just as any other school would. Just for the sake of argument, Joe was not administrative personnel (he ceded those duties when he stopped being the AD) so he wouldn't fit into that exemption. Even if he was "administrative personnel", his direct contact with 17 year old high school football recruits would likely satisfy the "direct contact with children" requirement.
It's certainly not who the statute was designed to cover, but under the definitions I see in this thread (again, assuming they are correct) I don't see a way that Joe would fit into the exemption. Curley, Schultz, and Spanier, though are different stories because they are administrative personnel who do not have direct contact with children.
Assuming you are correct about Joe, which I don't believe to be the case. When was this put in to place? I'm guessing not before 2001. It's extra moot because Joe didn't witness abuse, nor was he told of abuse.