The great myth that Akira Toriyama had nothing to do with DragonBall GT is just a flat out lie. He didn't write the story, and there was no manga. But the fact is Toriyama gave TOEI permission to continue DragonBall. He was the head supervisor for GT. He gave them input. He drew character designs for it, mostly the newcomers(Giru and the villains). Akira Toriyama also had involvement in the show's early stages, setting forth the initial premise of the series. So there you have it. All the facts you need to know. Thank you.
A direct quote from Toriyama himself:
Interviewer: So, you recommend GT, then!
Akira Toriyama: Yes! I recommend it. As an ordinary audience member, I'm looking forward to it.
-Interview with Akira Toriyama from Daizenshuu #7