Dan Aykroyd's character in Sneakers specifically mentions the moon landing hoax theory. Is this whistle-blowing? Of course not. Ayroyd and Sidney Poitier are the classic comedic diad in that film. It's a far more overt reference than in Diamonds, but in this case it's just part of the character.

I think we're expanding beyond the normal understanding of whistle-blowing. A whistle-blower is someone on the inside who has been entrusted with a secret, but who reveals it instead, ostensibly for ethical reasons. The sine qua non for a whistle-blower is that special, inside knowledge, not just what that person says. Someone who merely makes a reference but has no demonstrable "insider" knowledge is not a whistle-blower.

I believe Diamonds Are Forever is not a reference to the moon hoax theory. But it doesn't matter. It's irrelevant. There is no evidence that the creator of that scene could have had any inside knowledge. That kills the hypothesis right there. Ian Fleming is a plausible whistle-blower at prima facie. Richard Maibaum is not. Therefore there is no whistle-blow. Full stop.

All we have is an ambiguous scene in a somewhat campy film written by an unremarkable Hollywood screenwriter during the height of Apollo popularity three years before the first published moon hoax book. It's not clear that this scene even refers to the moon hoax theory, much less is trying to expose it. The holes in this hypothesis are big enough to fly a space shuttle through.