Whether it's true or not, always err on the side of caution with dogs you don't know. MOST of the dog people we've met at FW are great. But whenever you have that many dogs/people in one place you're always going to run across some people that are clueless at best, and completely inconsiderate and irresponsible at worst. Some people have no idea what their dogs are capable of - and/or the first time they've ever had them around other dogs is at the dog park at FW
In the 3 weeks we were there in Dec., DH took our younger dog to the dog park every day. There were LOTS of dogs of all ages/sizes/breeds and everyone seemed to be getting along just fine. They only ran into one dog that was not so much aggressive as just dopey and rude. He pestered the heck out of our dog (who was just trying to play with her ball) until the little princess gave him a quick "snap - buzz off!" and he backed down. Mind you, his owner watched all this without saying anything, and when our dog finally had enough, she just shook her head and said, "he's so stupid." All well and good, but had he done that to the wrong dog....
Our other dog is not great with strange dogs, and we know the dog park environment would just be WAY too much for him. He's not out to hurt anyone, but he can be a total butthead to other dogs, and it's not fair to subject anyone else's dog to that (or let him practice that bad behavior). So while DH was at the dog park, I took our boy over to the 300 dog walk where we could steer clear of the other dogs and still get some exercise.
Best advice is to know your dog well - what he can and can't handle - and watch them with strange dogs in the park at ALL times. Seriously - not even kidding. Bad stuff can happen REALLY quickly, especially if you're not an expert on reading dog body language to see the bad stuff coming (and sometimes even if!)
If you see anything that makes you uncomfortable, just take your dog and get out. Trying to reason with owners who are clueless about their dogs is usually an exercise in futility - as evidenced by the number of people I've had march up to me with their dogs on leashes who were snarling/growling at my dog while their owner said, "oh, he just wants to play!" <sigh>
And if you see anything totally inappropriate/dangerous, PLEASE report it to the front desk immediately! Disney may be quite lax about enforcing barking/obnoxious dog rules, but truly dangerous dogs are a huge liability for them, and they should be willing to address something like that quickly.