Dictating isn't collaborating, though. Those are completely different things, because the transcriber doesn't contribute anything creatively, just converts the writer's words to text. Dictation is simply an alternative to typing or longhand. Lots of solo writers have used it, including Cartland, Rod Serling, Erle Stanley Gardner, and J. Michael Straczynski.
So the method Shatner used to record his writing is beside the point. Either way, he wrote portions of the work and his collaborators wrote other portions, and they rewrote each other's words. That's how most collaborations work.