Am not sure if service in the Union Army by a Texas born citizen would be described as "Union Collaboration", but my great grand uncle, William Eden Kelcy, enlisted into the Union Army in 1862:

CIVIL WAR: Records show him as being: "Pvt of Phillip G. Temple Co A 1st Regiment of Texas Caverly Vol (Union). Was enrolled 20 day of October 1862, served 3 yrs discharged 31st oct 1865 at San Antonio, Texas. 23 years of age, 5'7', fair complexion, grey eyes, light hair, occupation: drover. 1st Texas Reg, Cav, had Col. Edmund J Davis, Nov 1862 & John L. Haynes, Nov 1863. Lt Col. Alfred F. Holk, Nov 1863-May 28, 1865." He was one of about 2,000 Texans who fought with the Union in the Civil War.