According to my server for the last trip, Disney covers all expenses on the ship (food, uniforms, housing, medical), provides them with internet access so that they can e-mail home, and provides all transportation expenses home for their vacations. However, they get very little in the way of salary, and basically work for tips. I was also able to confirm that if you charge your tips, they get all of it--Disney does not take a portion as a handling charge or anything.
Since they are not US citizens and the ship is registered in the Bahamas, they so not pay US taxes, and are not covered by US labor laws. Thus, they can work long hard hours for low wages, etc. Most of them are very happy. One server told me that he makes nearly 10 times as much on the ship as he could at home. Many of the servers, etc. are supporting families in their home countries. Others are young people out for a good time. I'm not sure how much they are supposed to tell.....but we have many "friends" who have been on the ship with us since the inaugural sailing!