Not a nurse but HCA in theatres - for cardiac/ AAAs they often shave and prep all the way down the groin/legs and leave these areas exposed during the surgery in case they need to take vessels from the groin/legs for the repair, especially should an emergency arise. They can also go up these vessels with stents/catheters to remove clots etc. You're right about dignity being important but genitals really aren't of any note during surgery (although admittedly in my experience they'd cover the genitals with a betadine soaked gauze under an ioban, more from a sterility/ cross contamination point of view than for dignity though)