Yep but Fightin Joe was the only Gen allowed back in and was made a Gen.
Actually there were at least five ex-confederate officers who later served as US generals, but only one - Joe Wheeler - is buried at Arlington.
Joseph Wheeler
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid= 6518
Matthew Cal Butler
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid= 9501
Fitz Lee
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=4660
Thomas L Rosser
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=11068
William C Oates
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=5901994
Joseph Wheeler: In 1898, Wheeler, aged 61, volunteered for the Spanish-American war, receiving an appointment to
major general of volunteers by U.S. President William McKinley
Matthew Cal Butler: During the Spanish-American War, Butler was appointed
major general of the United States Volunteers and was one of the commissioners appointed to supervise the evacuation of Cuba by the Spanish forces in 1898.
Fitzhugh Lee: Upon the declaration of war between Spain and the United States, he re-entered the army.
and was one of the ex-Confederate general officers who were made
major generals of United States Volunteers. Fitzhugh Lee commanded the VII Army Corps, but took no part in the actual operations in Cuba. He was military governor of Havana and Pinar del Río in 1899, subsequently commanded the Department of the Missouri, and retired in 1901 as a brigadier general, U.S. Army
Thomas L Rosser: On June 10, 1898, President William McKinley appointed Rosser a
brigadier general of United States volunteers during the Spanish-American War. His first task was training young cavalry recruits in a camp near the old Civil War battlefield of Chickamauga in northern Georgia. He was honorably discharged on October 31, 1898, and returned home.
William C Oates: Was only a Col in the CS service, but was made
brigadier general US during his service in the Spanish American War.