They're not basically midwives, midwives are medically trained and can deliver babies, write prescriptions, do most of what an OB can in an uncomplicated pregnancy and delivery (so no surgery or high-risk pregnancies). A doula is a professional support person, they're there to act as support and sometimes advocate for mom, but they aren't medical staff and (this story notwithstanding, apparently) don't do deliveries.

Editing to add: just read the article and one of the doulas in this story is also a licensed nurse, hence her helping with deliveries.