Well it happens all the time, but I think that most people (not just busy bodies) would not enjoy kids in diapers in their pool.
The term that I have heard before which comes to mind is "fecal teabags."
By the way, I have two children who are not potty trained and I would not even consider putting them into a public pool - even in the swim diapers.
Of course they go in my own pool, but that is because I am willing to take the risk of getting sick. But I would not subject others to that risk.
Chlorine can kill diseases and bacteria, but there are always problems with keeping the levels proper - that is why they have had to shut down water parks in the last few summers!