I'm not an expert so can only speculate weither my tips will be pooled among the staff on the ship or kept by the person or persons who give me outstanding service.
I DO believe however, that one of the best ways to ensure your staff person receives recognition for the outstanding job they do for you, is to include his or her name on your comment cards and maybe write a short personal letter to the head of his/her department praising them.
While this might not result in a greater share of the tips, if more people recognize the wonderful crew members and commend them for their great service, chances are they'll be the ones remembered when it's time for raises or promotions or even shift preferences. I'm sure any letters and comments received will result in a copy in the crew member's employee file.
Also of course, if you had terrible service, a written comment could be very effective in preventing someone on a later cruise from getting the same shabby treatment.