I recently was a Pace of Play official at Doral for the pro-am. I walked the entire round with Scott Hoch. He struck the ball very well.
He used a very narrow stance on every shot... maybe hip width with a driver... and had both feet perpendicular... no flare.
Later I watched a few other guys on this. Steve Elkington had his left foot flared out about 40 to 45 degrees with his driver. There were all kinds of variations on this.
I know this can influence Hip Turn and Hip Action.