For 2016[2], North Dakota had a poverty rate of 10.7 (10th lowest in the US). Of that 10.7%, 8% were listed as White.
Given this, I don't think a significant amount of Scandinavian-Americans in North Dakota are in poverty. I guess any number is not zero, but North Dakota is probably the wrong state to use for a demonstration.
1) http://worldpopulationreview.com/states/north-dakota-populat...
2) https://talkpoverty.org/state-year-report/north-dakota-2017-... https://www.census.gov/quickfacts/fact/table/ND/PST045217#vi...
Your reference [1] says that 30.8% of the state's population reports Norwegian ancestry, and 4.7% reports Swedish ancestry. Overall that's pretty close to the 1/3 I ballparked for Scandinavian-American.
1) I might still hold a grudge over the damn lefse and not being told its was potato before eating it. I was not in good shape 30 minutes later.
Assuming that the poverty rate is evenly distributed over the white population, then the poverty rate for Scandinavians would also be 8%.