You can find some photographers that are just starting out that might agree to do a destination wedding in exchange for cruise fare.
However, it isn't really a vacation for most photographer to do a destination wedding, as they have to be concerned about watching their equipment at all times, being healthy and getting enough rest to be able to do the wedding, then after the wedding making a backup and sending the images home on a hard drive for safekeeping, plus missing 4+ days of work in their offices and the chance to shoot other weddings at that time. Add in the fact that, on a cruise, they'd be unable to use the Internet to respond to potential and current clients, and you are taking them from their work for several days.
Additionally, many countries have restrictions about what kind of photo gear can be brought in, so if you are marrying in say, Mexico, the photog can only bring so much gear in to the country.
Also, the photographer may need to secure work permits to leave the country for work. This involves a lot of paperwork and going to the Embassy, so that costs money and takes several days as well.
Lastly, you really need to check with the ship's rules about bringing in your own photographer and videographer. They may have rules just as the parks do about outside vendors offering services.
I know many people just do it and go under the radar when photographing destination weddings, but experienced destination photographers do try to secure all the permits and permissions and that is complicated and costs money.
