though there are exceptions such as when LE has a good reason to believe a crime is underway or other criteria involving public safety, etc.  I would not think that any of them apply.

A good question is whether or not LE can convince the hotel staff to open the door for them.  Never heard that one mentioned anywhere.

It is possible that LE could get a warrant based on the ad and proof that the person who placed the ad is in that particular room, but that is an awful lot of time and energy and by the time they get it, hopefully the gal would be long  gone.  LE is not about to waste their resources on such a wild goose chase.

still not a lawyer

In general, you have some right to privacy in your hotel room - but not the same strict rights as you have in your home.  

The police can NOT enter your hotel room without a warrant, unless they have reason to believe waiting for a warrant will result in loss of evidence or danger to people (exigent circumstances) - and they have vast authority to make this judgement. Google "Brigham City v. Stuart" and "Kentucky v. King".

As for limited privacy: Hotel management generally has the right to enter your room without permission if they have reason to believe you are engaged in illegal acts, to stop you or other guests from destroying hotel property and for maintenance/housekeeping purposes. While you may need to permit HOTEL staff to enter in these situations, should they have police present you are under no obligation to admit the POLICE - the police must still have that warrant, absent exigent circumstances. Simply agree to let hotel staff in, and forbid police entry before opening the door - it may or may not work, as the cops have minds of their own - but it may help in a defense later. Google "Stoner v. California".

It seems to be pretty well established that a hotel may not reveal the room you are staying in to anyone, including LE, without your express permission. They may reveal the fact that you are a guest at the hotel, unless you specifically ask them not to do so... and have not signed a small print agreement that expressly allows them to do so as they see fit. Google "Motel 6 guest lists given to police".

My answer is that if police have probable cause (in the form of an online ad, identity and location) that a crime is being committed on a premises - they can get a warrant or notify the hotel and have hotel staff decide to enter. Not to mention the fact that some hotel staff are so poorly trained and some cops are so gung-ho; if they are there they are probably going to find a way to enter - warrant or not - and let the legal subtleties be settled in court.  

Nope. I'm not a lawyer, either.

I don't even want to get into the discussion about whether LE can enter the room without a warrant. My point is what would happen if they ever were to do so.

Sex with a hooker is NOT illegal. Hookers have husbands, boyfriends, and even random hookups just like any other woman. LE could kick the door in and catch you in mid coitus, but still would have no evidence of a crime unless one or both of you copped to either paying or being paid for sex. So IF this unlikely scenario were ever to happen to you, all you have to do is exercise your constitutional right to STFU and LE can't do a thing to either of you.

LE does not need a warrant if the hotel grants them permission. If you post your true photo and or send a true photo in any form of an advertisement / solicitation or potential solicitation you have granted "access" to yourself via probable cause. LE often refers to this as an "eye see" and may seek legal remedies to identify and pursue you. A hotel room does not grant you legal sanctuary for illegal activities (even if not illegal).  

Demographics vary widely on legal causes that LE utilize and abuse. They may do whatever they seek to do, regardless of the actual legality under any old thing they feel like slapping on a probable cause report. (sex offender,sex trafficker, trespassing, solicitation, prostitution, disturbing the peace, etc) Please do know, that if they are determined to get you for whatever cockeyed reason, they will. (Don't - not answer a door and give them cause to set you up for further chase)

Best to advertise and communicate within guidelines that you can afford to face in the area & community you work in.  
For example, what I do in freely Los Angeles or Anchorage is damned near public hanging in New Orleans and life without parole in Nebraska and Las Vegas.  

As a SW for 32 years, I mostly advise you to always behave in a manner in which you are perfectly willing to pay the price for their claims against you.  Understand that LE has a job to do and we are always on their shit list of victims to seize, legally or not. The fine points of the law do not apply to us. We are not among their classes and will be victims of their laws however they choose to apply them at any given time. Find comfort in that and you will sleep better at night.  
If you believe you are on the the "right side" of law for the sake of the actual written law then please find other career choices as this may not pan out in the end like you hope.

To answer your question directly, you do not have to open a door to anyone that knocks. But, the hotel can access them with a key. If LE is knocking and announces itself (even in a whisper) it is probably best to open and say nothing and take the arrest in silence and contact a lawyer.  Worry more for the total dangers of bad bad men that you might answer the door for. A misdemeanor B case is nothing compared to a few hours with a violent rapist.  

Warrants or no warrants are meaningless when you look at the entire picture. (as if a no warrant arrest would be dismissed or beaten in court by us anyways)

Be careful who you send your photo to that is attached to an actual given location. period.

If you are working in an arena whereas you are feeling that LE is knocking on your hotel incall door and you are fearful, then I'm truly sorry that this is your current circumstance and hope you can find your way to a more peaceful process. If you do not have other choices, please reconsider your advertising and communication habits to best protect yourself.  

Expect the worst of it. If the worst never happens, then you are lucky and have lived a better life for being prepared. Don't let them take your piece of mind. Take control. It's all up to you how this will pan out.  

Best of luck, truly.

Sincerely Sweet Sarah