The only thing we know for sure that Esau can do is take on the forms of the dead.
Then who was it who took the form of an older Walt and appeared to Locke in "Man Behind the Curtain?"
I don't think Esau would take the form of Jacob and appear to the Oceanic muppet babies. For one thing it would serve no purpose. They never met Jacob before, so why imitate him? He may as well have appeared as the guy from the beginning of the season finale, or indeed anyone else. The effect would have been the same.