I actually research prostitution during this time period. My book An Evening with Venus: Prostitution During the American Civil War was published last year.
Unfortunately, it is very difficult to know what was or was not taboo among prostitutes. The sex workers themselves left very few written records of their business. Most of the records that they did leave have to do with their life circumstances that lead them to the sex trade.
Likewise, most customers didn't specifically note what went on during the transaction. It was fairly rare to write in a letter to friends or family that one went to see a sex worker. Even then, most of the time it was just a general mention that the person went to a brothel.
That said, most likely it was an acceptible act especially among prostitutes. I've never seen anything about any specific acts being forbidden. Most of the time, women of the time became prostitutes out of despiration. With that in mind, I can't imagine them turning down a paying customer for something "icky."
I'm (somehow) new to the sub. I hope I can ask a question in the comments real fast: Was oral sex something not performed in a normal relationship?
I remember this coming up in a Freakonomics discussion and I managed to track down a source.
Something from a bit of a later date, but in Slumming: Sexual and Racial Encounters in American Nightlife, 1885-1940 by Chad Heap, there is some discussion of fellatio and the author states that it was considered "unnatural" or "foreign" by most Americans at the time. The euphemism for the practice was "French".
He goes on to say that in the brothels where this was offered, the other prostitutes would shun those who offered the workers who did offer the practice, refusing to associate or eat with them.
I would speculate that if in this time period it was considered unnatural and foreign to offer such services, it is possible that in the "Wild West" it may not have been offered.
Edit: Here's the Google books link to save everyone time: https://books.google.com/books?id=Pcs6T-NVz0wC&lpg=PA136&ots=2H8nIIkKnL&dq=chicago%20brothels%20french&pg=PA136#v=onepage&q=chicago%20brothels%20french&f=false
Can you define a little more specifically what you mean by the 'Wild West?' Any dates in mind?