You're assuming it's a conscious thing.
As they just established in this episode, Nature chakra is not, like, this weird thing you need to know how to use. Sage mode lets you collect it, but once you have it, you can do all the same stuff with it that you do with normal chakra.
After all, the Cursed Seal is Nature chakra, and Sasuke could use it just fine without knowing a damn thing about Sage jutsu.
Edo Tensei could function the same way. The jutsu itself draws in the Nature chakra, and the zombies just use it the way they would any other chakra.
He probably could, but again, why would you WANT to?
They haven't shown a single advantage a living human has over a Reanimation. The only real downside is being under control of the user, but I suspect that if the user wanted to, he could let an reanimation be completely under it's own control.
I thought this up ages ago, but the smartest thing you could do, since Edo Tensei doesn't dispel when the user dies, would be to create an animation, and command it to perform Edo Tensei on you, you kill yourself, the animation brings you back, then you dispel your Edo Tensei, destroying that reanimation, leaving you reanimated, and the person that reanimated you is gone and thus there's no way to release the jutsu animating you.