You can absolutely hunt with a single pin sight, but it does take some extra skill to master. Because single pin bow sights offer only one fixed range setting, the user has to manually move the pin to the required yardage before their next shot. Otherwise, they will have to count on their shot being the same distance every time. Obviously, this is not ideal for hunters in active trailing situations.
Some bow hunters have become quite skilled at using a single pin setup to estimate different yardages, but there is no arguing that a multi-in setup is the way to go for serious hunting.