Assuming even a high class escort has sweaty sex with at least 6 obese middle aged men a day, that's a lot of chances for her to catch HPV or The Herp Derp from skin on skin.
the risk of catching HIV from raw dogging a $200 'nursing student' is about as high as winning the lottery... but you have a much higher chance of catching an annoying, never ending STD... and you don't want to be dealing with a monthly breakout on your junk for the rest of your life.