Their has never been any proof that he scripted the wookie battle on the fourth moon of Utapau, or that The wookies were trained by Ben and Luke to attack the Death Star.
They may have been ideas but they were never written down.
I always thought the ewoks were put in the as a fairy tale motif Like Obi Wan Being in Star Wars, Yoda in empire Strikes Back etc.
We will never really know the truth of the matter but i am sure yoda and ben came from joseph campbell, and the ewoks from the brothers grimm and Bruno Bettleheim.
I have always thought the Ewoks as the Viet Cong and the Empire as the United States was always complete bs. I mean the battle is turned only when they steal that at-st and use the empire's technology against them. There sticks and rocks do little to nothing. Yeah, George has said it is about the Human Spirit and all and i get that but he may have fudged things a bit there.