I'm sure that there are a fair number of providers checking in, but most hotels are doing quite a bit of business -- at least 50 different clients per night, and usually more (sometimes a LOT more). There are also regular guests who are checking in for their own purposes that might not welcome overly inquisitive staff. Assignations between cheating spouses are certainly not uncommon, and visiting businessfolk have been known to let their hair down a bit, too.
High traffic along a certain floor might draw a little attention, as might unusual check-in times, or late-night visitors. However, unless someone complains, the hotel isn't losing anything by having a guest who is knocking boots, even if she's being compensated. Discretion is important -- if she checks in wearing a bustier and stripper boots with a pimp in close attendance, that's a bad sign. If she's wearing a sundress and flats, or jeans and a polo shirt, that's a whole different story.
It also takes a while to gather evidence, and the smarter ladies aren't in one place for very long. If someone stayed in a hotel for several days and was conspicuous enough to draw complaints, then somebody might call the cops... who would then proceed to try to fit a misdemeanor investigation into their schedules, and collect evidence, and then try to make a bust happen. Housekeeping might look around the rooms a little and report back, especially if someone thinks there might be drugs involved. Still, it's going to take a while -- a couple of days certainly, and probably at least five to seven days to make everything happen.
If everyone is treated well (no complaints to hotel management, the housekeeping staff is tipped well, and nobody calls the cops), there's not likely to be any problems. If someone gets their back up about something (management has to deal with a drug-dealing pimp roaming the halls, or a guest reports raucous sex at 4 AM), then you might run into problems. If nobody is making a fuss, then there's little motive for the police to press the issue -- after all, this is generally a misdemeanor, unless there are minors or drugs involved.