Someone else posted about this and the advice given was to not really sweat it.  People come and go and often time business is conducted in hotels so its not so "strange" to see people who haven't checked into the hotel go.  Often enough, people get visitors because they are visiting the town for a bit.  So if stopped, you could simply say that your visiting a friend who is staying there.

Don't even give it a second thought.I've never been in a hotel,as a guest or to rendezvous, where a staff member asked where I was going.Just act like you're a guest that's staying there and walk as if you are.There's way too much activity and too much concern over their own jobs to worry about why you'd be there.Besides,do you think that they think that you're the first guy entering their hotel who's not there to sleep? You've been watching "The Graduate" too long. LOL! Good Luck!

just walk in with a small garment back over your shoulder or carrying a briefcase.  Have your cell phone up to your ear and pretend you are in the middle of an important conversation.  Keep your eyes ahead, don't stare at anyone but don't be afraid to look them in the eye and just nod hello.

Walk straight to the elevator, stairs or hallway and go to the intended room.  As was stated, you will be fine and very unlikely anyone will say anything to you besides "hello sir"

The above advice is solid.  I try to think of everything that could go wrong and have a plan, course of action, or response in place in case it does.  But, I've never had your specific worry.  I'm not trying to insinuate that you're the world's biggest worrywart, nor am I trying to be cold.  But, you may want to stick to apartment incalls since that has worked for you.

I'm not a newbie, and have a number of incall hotel/resort appointments, and have asked ladies visit me in hotels, and have never had a problem.

One of the lady's tactics to avoid problems, is to know the name under which you are registered under, in addition to your room number.  That way if ever questioned, they can honestly say that they have a business appointment with Mr. X in room 123.  Is it fair to ask for the last name under which she reserved the room?  I know, a bit over the top (and somethng I've never requested), but for someone with myreality's concerns, I'm sure it will provide him with greater comfort to be able to say, if challenged, I have a business appointment with Ms. Y in room 321.

Just curious.

Now some real advice,
if you have these concerns, ask the lady to meet you in the hotel bar, dressed discreetly, of course, this way there is no question that you are welcome to her room.

I am more nervous going to apartment house locations.  I always worry about the neighbors noticing a lot of foot traffic to a single unit.  Every apartment building seems to have one resident that wants to know everybody's busuness.