According to the obit of his daughter Mary (1844-1919), wife of David Dietz, George Thomas was killed in the Civil War and buried at Arlington National Cem. A search of Arlington burial records at Ancestry.com on 27 June 2006 showed every George Thomas buried there died after the war, except one, who had no dates listed and was buried in site 2498. Ancestry lists 200,064 burials at Arlington, but Wikipedia reports that more than 260,000 are buried there, so Ancestry's records appear to be incomplete.
George and Rachel Thomas apparently did not marry. Rachel was only 15 when Mary was born in 1844, and was married to Henry Roseman by the time of her daughter Rachel's birth in May 1850.
Assuming George Thomas is from the vicinity of northwest Somerset County (where most of the Thomas family does come from), one candidate is the son of George (of Christian) and Eve. This George was in the census age 20 in 1850, in Conemaugh Twp, Cambria Co, and age 27 in 1860 in Shade Twp, Somerset Co. At this date I have not found him in the census after 1860. If those ages are correct, he may be too young. This George Thomas is supposed to have married a woman named Lucy, but I have found no record. The Mishler tree says his wife was Lucinda Mishler, and they were married in 1854 in the state of Indiana, but I am confident that the 1860 census in Shade Twp is the correct one, and there George is single living with his widowed mother.