For our Alaska trip it was DH and myself. We sat at a table with 3 other couples. None of us tipped the server, the ast. server or the head server. They were all pretty stinking. It was something discussed by the couples prior to dinner to see if we all felt the same way about the service and we did. Things were horrible on that one. But we did tip the "mint" guy, he was outstanding.
Now speaking from experience the servers do make a decent weekly wage. That most of them send home to family or save because they really can not spend it on the ship. Their tips however are split. So if you tip the server it is split between the server, the dishwashers, and the cooks. In my opinion $25.75, which is the suggested tip is not enough to split with 3 people. We normally go with the base amount set aside and then tip extra if the service is worth it. We always tip the room people extra.
Now the housekeeping people do split their tips with the people behind the sceance that wash the linen.