On his WW1 registration form, Harold was living in South Dakota and was married to Fannie Jane. He was living in Wilkin, Minnesota in 1942. He could be the Thomas aka Harold Ellis who died in Minnesota on 13 Sep 1942. 
"United States World War II Draft Registration Cards, 1942," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:QKCC-MBNY : 14 April 2016), Thomas Harold Ellis, 27 Apr 1942; citing NARA microfilm publication M1936, M1937, M1939, M1951, M1962, M1964, M1986, M2090, and M2097 (Washington D.C.: National Archives and Records Administration, n.d.).
It may be possible to confirm family relationships with Thomas by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
However, there are no known yDNA or mtDNA test-takers in his direct paternal or maternal line.
It is likely that these autosomal DNA test-takers will share DNA with Thomas: