In order to perform any jutsu you need to perform proper handseals to accompolish the result. Kabuto needed to know the hand seals for ET provided he should also make himself aware of the reanimated soul's skills, too. If these two conditions are provided, ET can perform better (I did say better, not the best). Remember Kabuto was recalling the skills of Nagato ET while he confronted with Naruto, Itachi and Bee.
ET is a forbidden jutsu and the first person to use that was Second Hokage (Nidaime). The result was much better when Orochimaru performed it, but it didn't give optimum result.
Kabuto's ET is kind of weird as he gave some liberty to reanimated souls. They can think as long as the jutsu controller doesn't control their mind. In this case they were allowed to perceive the world and react to it. Therefore (and this is the important part) if the reanimated souls motive is similar to the person performing ET (in this case, I am referring to Kabuto), then performer's work for controlling the souls would be less and easier as soul's motive and performer's are same.
Kabuto's ET was scalable, too. He was sitting in the cave and visualizing the entire war scene through Reanimated Soul.
By which I conclude that even if the mind is reluctant towards ET, their physical movements will always be under the control of ET [this was the common denominator for all ET performers (Nidaime, Orochimaru and Kabuto)]. Remember the Zabuza's ET where he told Kakashi that he can't control his movements although he was barely able to think? Same goes for Asuma's ET, too.