Sean,
Again, as you would suspect, if a golfer can't extract the sand all the way to the green, the green won't be impacted. On deep steep faced bunkers, what takes a beating and ends up changing are the bunker faces. The grass can die from the sand build up and the sand line can creep up the face on less well maintained courses. As someone said on a different thread, sometimes grass faced bunkers can be more difficult to maintain than sand faced bunkers.