I'm a detective here in New Orleans. All passengers aren't checked to see if they have warrants, because thats a totally independent computer system that you'd have to run them through (its call NCIC and ARMS). Don't believe the hype. There are no 'sweeps", but people are going to believe what they want.
Quick story, which relates to this thread: One of the detectives I work with found out a guy had committed a string of burglaries, and when he went to look for him he found out the guy was on a cruise out of here in New Orleans. The detective found out when the ship was returning and was there to "greet" him.
And on a sidenote, there aren't "quota's" on traffic tickets either. In case you thought there were. ; )