Disney's workforce within the WDW parks alone is large enough to constitute a small city. Nearly 70,000 people is a tremendous amount of people. I have no idea how many people work for Universal or SeaWorld or any of the other smaller tourist attractions, but I would wager than nearly 1/3rd of Orlando's population are in Orlando and living there because of tourism and/or theme parks.
That said, the odds of a massive sting operation online is very likely to snare a few creeps that slipped through the cracks. There is almost nothing Disney, or Universal, or SeaWorld or any of the others can do, especially if said offender(s) are of the first-time offender variety, or simply just hadn't been caught yet.
From the evidence presented in the story, there were dramatically differences in deviance exhibited by those that were caught in the sting, but not a single one of them had a prior offense of any kind. That really doesn't give the theme parks any cause to deny their hiring if they haven't been found guilty of the crime. Without adopting some method of profiling (which is a big ethical wormhole of never-ending debate), there is only so much that can be done to protect park-goers with hiring policy.
To use an analogous situation; a drug policy is always in place in every workplace to protect the consumers and protect the company from liability. But when you're hiring thousands or people per year, you can bet there is going to be a veteran drug user that knows every trick in the book to stay off the radar and pass all their screenings.
Personally, I have a very Draconian sense of justice when it comes to predators so I'll just leave this as a thought on hiring policy.