It's been established that you can still embroider names on hats, so it's got nothing to do with safety concerns. The warning against putting the child's name on clothing seems to be because a predator could more easily lure the child away by knowing his or her name. Maybe, but I am not currently aware of any actual cases where a perpetrator used a child's name in this fashion. This seems on a par with the warning that parents should avoid having those stick family decals on the back of their car as it may alert predators to the presence of a child. Predators know where to find children if they want to, and they don't have to know or use their names - they could for instance ask the child if they want to see a puppy or kitten, or say the kid's mother was in an accident and the kid should come with them (Ted Bundy abducted a 12-year-old girl from a schoolyard using this story)
Children old enough to understand should be cautioned to never go anywhere with anyone they don't know, no matter what the person tells them, without alerting a parent or someone in authority. At WDW children should know how to recognize a cast member with a Disney name tag.