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?