Federal records archivist here. We can't know the answer to that for sure, we aren't privy to details of Reagan's medical privacy. Most classified topics concern technical details of aircraft and weapon design, or other things that would hardly ever come up in conversation unless you were at work. It's unlikely that it was ever an issue, and if you've ever been around an Alzheimer's patient, you know they say a lot of things that aren't true and don't make much sense, sadly. If it did come up by some chance, the family would just sign a non-disclosure form, probably.

Maybe the moderators will let it pass, but this question technically violates the 20-year rule (Reagan was diagnosed in 1994, and your question would concern events in the years after that).

It's an interesting question, though.