Not sure about that, since the narrative never was that enemies of the WG for mysterious reasons get sick to broadcast it to the world. They just execute their own kind or cast them out if they happen to misbehave. I don't see how Ginny would've become a danger to them either if she and the respective Celestial Dragon happened to develop some kind of relationship, especially a one sided relationship. I also doubt that the CD developed some kind of intimate feelings to her, given she was cast out like trash once she was "useless".
But yes, good catch with the Sapphire, which could be a hint that Saturn might have infected her.
As for Roger, I do not believe that his sickness had anything to do with Saturn. Roger developed his disease 10 years after the God Valley incident. And after that, Crocus could keep him alive with meds for the rest of his voyage, and that sickness didn't seem to have any visual effect either. Also, we know you can break through DF hax with Haki. Law did it against Doc Q's disease without even having CoC and without having particularly powerful CoA, while Roger was basically the peak of Haki, especially CoC, which is willpower.
So I doubt, that Saturn somehow infected Roger without really encountering him (as Roger was busy chasing Xebec), with a disease that only got triggered 10 years later and Roger was unable to dispel it with his incredibly powerful Haki. While still giving him enough time to complete the voyage, sail to Laughtale and start the era of piracy.