Housekeeping is one of the very few disciplines within which there is a discrepancy with respect to whether tipping is expected or not (at least in the USA). If you go into a restaurant or take a taxi you know for sure that the server's compensation is wholly dependent on tipping -- that the server may not even be getting minimum wage without tips. Similarly, you know that chefs, security guards, etc., are not tipped personnel. With housekeepers though, it actually DEPENDS. Many national chains pay their housekeepers based on the priniciple that tipping is expected, while still other national chains pay their housekpeers based on the expectation that their salary is their only income. Some require tips to be refused politely, and if that doesn't work to deter the tip, require the tips to be turned into management. (Perfectly legal, folks. Tipping is not required by law, and so if a business pays minimum wage and has a no tipping policy, it's perfectly legal.) Since even national chains differ about this, you can be sure that independents differ as well.
So the only way to know is to ask management at the hotel.
I believe it is very clear that all *cruise ship* housekeepers are compensated primarily by tipping.