I don't know how common the donut thing is but they would have to be organic donuts for an organic dairy
On the GBS complication from campylobacter, it's a 1 in 1,000 chance if you have a campy infection. Quite a few raw milk dairies have had campy outbreaks, including Organic Pastures and Alexandre Eco Dairy here in California. I don't if Alexandre was pasture-based but its owners are WAPF chapter leaders so I doubt the cows were getting many donuts. In any case, campy is out there in the world and GBS is 1/1,000 if you have campy.
You are far more likely to get campy from undercooked chicken than from raw milk, but chicken isn't usually linked to outbreaks because people tend to eat it well cooked.
Amanda