Yes, it is normal.
You will see it on many helicopters, particularly the bigger ships, with sheetmetal tailcones/tailbooms. Smaller machines tend to have semi-monocoque or honeycomb panels which offer much greater rigidity through their design. On the big machines the tails are manufactured with conventional construction techniques, as the physical dimensions, drivetrain requirements and thrust to be absorbed are so much greater - and the necessity to limit weight becomes more significant.
It also not unusual to find skin cracks in these structures as the skins relieve themselves. These cracks tend to appear in the same location on all the aircraft - not surprising really!