I have taken cameras on cruises with no issues, including SLR's, range-finders, end even cameras we don't speak about on this board. I am old enough to remember when almost all US cruises had Kodak ambassadors on board. I have never been asked to stop using my cameras.
There are several things to keep in mind.
1) there are a lot of scantily clad women around the pool area, many of them minors, so judgement and discretion are in order.
2) most "street photo" type shots will be present on shore. On the boat, you will find lots of harried people waiting in line.
In general, a rangefinder will identify you as a tourist photographer and you will likely be left alone. A nice appearing SLR will be confused with the D-SLR's used by the cruise photographers and you will likely be left alone.
As long as you stay out of the way, and don't appear to be stalking individuals, you should have no problems.