It's more like something a manager does to pick up cash...  he knows what it's for...   I know there are some that do but I doubt that corperate condones it.  

Seldom a concern for clients...  I book ladies with incalls.  I have run accross ladies that apparently rented rooms just for the time of our meeting...  but do not know how they arranged it.  
H

Most hotels are not really set up for an hourly rate structure nor do they want to attract that kind of customer. With the "name your own price" option you can find rooms for $30 or so on up at pretty decent hotels.  It may not be an "hourly" rate but you will get the room for half price and sometimes less if you are flexible with your plans.

I would not expect the large chains to have hourly rates.  An exception might be near an airport, for people traveling on business, might give you a half day rate so you can rest, and maybe take a shower.   I do know from personal experience, that sometimes providers will rent a room for just one client.  When I encountered this situation, she asked me how she should vacate the room.  She had paid ahead in cash, and I told her just leave the key in the room, walk out like you were going somewhere.  You just don't come back, they will never know.   The bed looks like it has been slept in, they got their money.  They could really give a shit whether or not anyone actually spent the night in the room.

Swim

Hotels that have hourly rates are ones you do not want to stay at. except ...

Day rate is a different story. A lot of times, business people want a place to crash between appointments (or long layover if it is near an airport), or to interview people during the day - thus the legitimate demand for a day rate.

"Romantic" hotels, like the Sybaris Inn,  offer 4 hour rates during the day.

You can get great rates on Priceline and Hotwire. The only problem is if you want something around Noon. Officially, the check-in time can be 3pm or later, and check-out time can be as early as 11 am.

If you are getting a hotel for yourself, I don't see any harm if you just happen to mention to the guy that you are having a rendezvous with your girl friend. One problem might be is when they get to know you, and she is the 5th girl friend you have met.

A  lot of airports now have hotels in the airport itself that rent by the hour, or, say, by three- or four-hour blocks of time.