From what I have read at the end of the cruise EVERYONE puts all the money they received in their envelopes in the middle of a table and then it is divided up according to some unknown set of rules for who has the most service time down to the least amount of time but everyone gets something. So if you tip your regular wait staff in the main dining room their expected tip amount, that person serving you the pizza will ultimately get his share of the money for the services he rendered to you.
Tipping is a sore subject with me though. I believe in a tip for good service but I also believe that the cruise lines should pay their people more to begin with even if it meant that cruises would be more expensive. Then, you would have the cruise lines offerring more competitive prices and more "real" deals instead of the b.s. deals you hear about but end up costing you 10x more than advertised. AND Then, when you DID get good service from your cabin steward or wait staff you could tip them accordingly and it shouldn't have to be divided up. The cabin steward or wait staff person who didn't earn a lot of tips would realize that he/she must not have been doing a good job.
As it is now, what incentive is it for the crew to do an outstanding job when a "slacker" is going to get included in dividing up the money? Just an observation. But again, I do tip well because it's not the crew's fault the system is screwed up.