We aren't supposed to cross-post to other forums here. But maybe after your query has gleaned responses from this one for a while you could ask the moderator to move it to Travel Photography. Maybe you might hear from somebody additional there. Meanwhile, you could also read through that forum. If you noted somebody there was a cruise photographer, you could PM (Private Message) him/her.

I know the people working cruise ships sign contracts for various lengths. You might suggest your nephew sign one for the shortest time possible, to test whether the job works well for him.

I understand the rooms for crew are really tiny. I believe they are shared. Some ships have crew eat in the same area as passengers. Not the fancy dining rooms, but the buffets. Some feed them in separate areas.

I suspect the job is like many others - works really well for some people, so-so for some, not at all for others.

I know crew members seem to be able to get off at ports, although there probably are jobs were this isn't possible.

Has your nephew ever taken a cruise? If not, and he lives near a cruise port that does the short 3-4 days cruises, it might be good for him to jump on a bargain rate one and learn a bit more before he signs anything.