I think so. Perhaps it's because creative people live in their own world. A world where they set the limits; where they say what's "normal" and what's not. The "normal" world has many pressures to conform, and creativity can't conform; it must be free. Because of this, many creative people have a hard time in the "normal" world (ex. relationships).
Now "insanity" is just how others perceive it... A creative person's mind never slows down - 24/7. There's no pause button, and no way to slow it down. They think and speak in stories. They're always in a cycle of creativity (up or down) - which can lead to heights of ecstasy and depths of depression. They tend to be more emotional (ex. crying for no reason). Does that sound like a "sane" person to you?