Do escorts usually ok this (uncovered on the stomach or breast or backside)?  I guess it would have to be discussed when setting up the appointment or can I wait until she's there since I would not want to talk with an agency about it.

You should talk it over with her when she is there. Do not ask the agency as talk such as that might be taken that you are a cop. I and many of my escort friends provide that service but not all of us are the same. Some of them do not like it and might find it offensive so you need to talk to her before the session starts.

I would advise that one not discuss ANY specific act while setting up the appt. You are better off to inquire once you have started a session and both of you are "comfortable" with each other to begin discussions of that nature.

"do escorts usually ok this", some offer it willingly, others decline, and of course YMMV. I could only offer that you research reviews, or maybe ask a lady you have met before that trusts you.

First frankly if I am asked about something when scheduling session then there will be no session.
Next that is something that is only safely discussed after the session is begun and both parties are safe then it will vary on the provider. On a personal note, I sort of enjoy watching a man cum.