I don't stay on property, so I don't deal with EMH, but I'm pretty sure there's no such thing at the water parks. We're big fans of the water parks and have never noticed it.
You don't need it anyway. The water parks usually don't open until 9 or 10am, so making it for rope drop is easy. You don't need to show up an hour early, 10 minutes early is more than plenty. The first 45-60 minutes the park is open, you can ride any slide you want with little to no wait. We've done Humunga Cowabunga four times back to back. The biggest challenge will be running up the stairs so many times in a row...you'll get tired.