Do they use an IV with general anesthesia for wisdom teeth?

Yes. It is easier to use an IV for the administration of sedatives.
Yes. Normally general anesthesia gets started through the use of an IV , most of oral surgeons offers IV sedation as well .
Yes. If you have a general anesthetic, you will have an IV started for administration of medications and fluid replacement, many oral surgeons offer IV conscious sedation as well as general anesthesia for their patients undergoing the removal of wisdom teeth.
Usually IV sedation. Discuss your particular circumstances with your surgeon for more specific answers and the options regarding local anesthesia, with or without "sweet air", or IV sedation. General anesthesia is seldom used anymore for the removal of wisdom teeth.