I've spoken to some of the staff on several ships regarding their tips. Not one ever told me they don't receive their percentage. They did tell me if I tipped more, they had to pool it and share with the others.
Mary Lou Scanlon
NCL Pride of America April 24, 2010
NCL Epic February 12, 2011
RCCL Allure of the Seas - September 18, 2011
Celebrity Eclipse - February 11, 2012:
RCCL Navigator OTS - February 9, 2013