The 10% fee that NCL charges is a service charge and not a tip. YOU MUST STILL TIP on top of that. My understanding from multiple sources is that the crew doesn't receive this as a tip and the end of a cruise. They still expect you to tip for good service.
I was on Pride of Aloha a few weeks back and we discovered this three days into the cruise.
I think it is criminal for NCL to advertise a price and then to add a 10% service charge on top of that and make it sound like it's a tip pool when it is not.
Don't screw the staff on NCL cruises ... you need to tip.