Many RLD girls certainly do allow oral, but when you say 'oral' I assume you are referring to your mouth and/or tongue making contact with the girl's pussy. As you can see from my most recent trip report ( Hungarian Honey -
http://www.ignatzmice.com/WWWBoard/PHPB ... php?t=6360 ), and in fact all my reports, it is not always the kitty that is my intended target for my own oral pleasure.
One important thing, however, is to make sure she understands exactly what your intentions are, despite how mechanical it can appear at the entrance to her chambers discussing such things. But I ensure that what I require is both explained and understood before I wave goodbye to my euros.
I always take a regular mouthwash with me and use it afterwards, also avoiding brushing my teeth too soon after. This is certainly no medical statement proclaiming safety, as with all sexual contact there are risks, but I feel these minor efforts benefit my own well-being, even if only mentally.
I have personally never contracted disease or ailment from a prostitute (to date), but have had my fair share of irritating issues in my lifetime which have, in some cases, required the intervention of antibiotics, but these have always been from what you might term as 'regular' girls. Girls in the RLD, IMO, take more care with themselves than many.