Dug for gold today and got a wheelbarrowful of sweet potatos from two (3?) plants that survived of the 9 planted long ago. The one plant with the most and biggest was in the hugelkultur bed. It had sunk so low I was digging up 2 ft bits of rotting wood or a 3 foot branch when I suspected I was pulling up another string of foot long tubers.
Can't truly say the hugelkultur helped the sweet potatos in that bed do better- think it was closer to where I was watering once in a while!
My experience with sweet potatoes seems to indicate they like nice soft deep soil, so a bed where there are obstructions like logs might not be the most productive for them unless the logs are covered with a lot of nice soft deep soil.
I grew them in the berm of a swale this year and got my best crop yet. A good yield despite the fact that I didn't add any manure or other nutrient source save for woodchip mulch and the soil is very depeleted of nutrients. Which confirmed what I've read about sweet potato not needing rich soils.