In another thread this was posted. I did test it and it works:
I lucked upon a way to play Hulu Plus from my iPad to my Apple TV. I can launch Flixster, start watching a trailer, hit the Home button, launch Hulu Plus and pick a show to watch and it plays on my Apple TV. This didn't work trying my Videos app first. So far it only works by launching Flixster, watching a trailer, then going to Hulu Plus. Seems to stay connected until I completely close Flixster or Hulu Plus.