Off the top of my head, I'm not aware of any "scientific" studies, and I doubt there are any. The PFI certainly isn't going to do a study on it, so unless Dr. Pierson or someone like her has done a study of their own, something like that probably doesn't exist. That said, the person who asked the question can do a little "experiment" of their own: put some kibble on a plate and moisten it, then leave it out for 24-48 hours in a place that's at room temperature and where the cat(s) can't get to it. After the time has passed, they should look at the plate. They will see the mold/mildew growing on it.
And that means that it was growing even before the time passed, it just wasn't visible to the naked eye yet.
I would also point out to this person that Dr. Hodgkins has done a study of her own that found that diabetic cats on wet food diets either went off their insulin or significantly reduced the amount they were on, compared to cats on kibble. It's not just about the moisture, it's about the high carb load. Adding water doesn't help with that, nor does it increase the amount of animal protein that cats need.
I hope this helps!