Condoms don't protect the wearer fully in any scenario, it does not protect against genital ulcer diseases, only protects against certain HPVs effectively, and doesn't even offer full protection for sexual secretions.
They also do not protect against even a small percentage of common comunicable diseases which are risks to anyone that even touches other people, let alone has sex with them.
Condoms also don't protect against anything 5% of the time anyway because they often times fail even if used correctly and before expiration, so there really is no way to be fully protected.
Thats why on condom wrappers it says:
"latex condoms may reduce, but does not eliminate, the risk of pregnancy and the risk of catching or spreading HIV"
Condoms are for reducing the chances, not eliminating them
Also if were talking about people who are getting paid to have sex, then I think its safe to say their sex acts might involve more then just strictly vaginal intercourse with protection. So if they participate in something like anal sex, fellatio, cunillings, or any other alternative, then the risk only increases.