If you know your way around in Vue, you can achieve a close looking environment like in Avatar movie - especially those floating rocks and the mist and clouds hovering around.
Gill did a good job in her render - but for sure, she can get even closer and closer to the movie look, putting more work into it.

Anyway - they didn't use Vue in the Avatar movie, because they've programmed a system, which was capable of growing plants instantly and interacting and influencing each other ... because they needed this for a real time movie and not a still.
So the requirements for landscape and plant design were totally different and Vue, as nice stuff you can do with it, wouldn't fit in the pipeline.

Sure, i can't and don't know either, what programs they've used, i've just read a few detailed articles about it and there was never Vue mentioned in there.
Vue could've been used for quick pre-screening purposes in early developement stages, who knows - but maybe in the future there will be more information available in this matter.