When they say laminate, I think of a man-made material that might not be too strong as compared to wood. for wood, the 3" hole would not be a problem but with some laminates it might weaken them. One way to feel better about this would be to lay a second layer inside the laminate back. Is there space where you could cut a board to fit, glued and fastened inside the laminate back? If so, cutting the hole through both then will not hurt the strength at all. Make the holes in a place a bit away from the edges of the laminate so that if it does tend to crumble a little it will not reach the edge of that section. A hole in it does no harm but if it crumbles too far,---- that's bad!