How do complementary doctors treat prolonged labor?

Unsure. I have no knowledge of a complementary doctor providing intrapartum obstetric care. The length of the labor is directly related to labor, delivery, and postpartum complications - so a prolonged labor does need to be managed in some manner to expedite a safe delivery, for both mother and baby.
Multiple ways. If the labor is not "active" and is early stage non-progressive labor often ob's wait for "mother nature" to get in sync. Prolonged active labor that is not progressing with cervical dilitation and there is a pelvic bone obstruction present than surgical intervention will occur(c/section). Contemporary ob's rarely use forceps, or stimulate a labor with meds if the fetal monitoring shows a problem.