I think Dan's point was more that by opting out of the auto-tip, what you're doing is actually not helping those individuals you're seeking to reward. When you do that, anything you give to them must be turned in and is then distributed amongst the general tip pool. They do not get to keep what you give them directly.

If you really want to reward individuals, then you're better off just leaving the auto-tip in place (consider it part of the cost of the cruise), then tip those people in addition to the auto-tip. When you do that, they're allowed to keep what you give them.