The head server and the dining room manager are 2 different people. THere is one dining room manager for each dining room. You generally will not see this person except that he is one of the guys standing by the door when you come in, and he is not a suggested tipping person.
The head server is the "boss" over a group of about 10 servers. There are about 3 head servers in each dining room, one of whom is assigned to your table as the supervisor of your server and assistant. You SHOULD see this person each evening. He/she should come by just to ask how everything is and to give you a chance to ask questions or make special requests. In addition, he will sometimes come by to help out your server (if he's a good guy....like when your server has 20 lobsters to crack open). This is a tipped position--the suggestion is $6.50 on a 7 day cruise. IF you never meet this person, by all means, skip his tip. He didn't do his job. If, on the other hand, your DD had requested a chocolate birthday cake (instead of the standard white) and he has arranged with the chef to meet this request, then he has earned his tip. If the flowers that your husband ordered show up at your place at dinner, he has earned his tip (he took care of this). If he comes by and asks if you have any questions about the island you are scheduled to visit the next day, etc....he is earning his bucks. Bottom line, if you speak to him each night he is doing his job. If he comes by on the last night with his hand out and that's the first time you've seen him, you don't owe him a thing.