That’s what I thought as well... but Hulu is on each of our Unlimited Freedom lines as individual accounts. When Sprint’s customer care people added it to all the lines on their end, it sent a separate sign up text to each line, which meant a separate Hulu account for each line was created. Not sure if this is the case for others, but it’s what happened for us.
As far as the charge for Hulu for other plans, I saw Tweet replies from customer care that any Unlimited Data plan qualified for the free Hulu offer. Perhaps that was in error?