The vengeance kill happens at night as a formality - in literal terms it should happen just prior to the lynch. Which means it's still day time. Which means a roleblock attempt should not be able to happen as it is a night action. If we were to say alright the roleblock is a day time action too, then it should be witnessed by the crowd of people standing there. I'm under the impression that the actual function of the Prostitute is to sleep with someone so they forget to act. Sleeping with someone until they get hung doesn't sound very viable and in front of that crowd you would be witnessed and your role revealed.