I suspect in reality that Texans in the early 1860s were much like their grandfathers, the American colonists in the 1770s. One of my (college) history profs once offered that "...about 1/3 of the colonists were rabid patriots, 1/3 remained loyal to their king and the other 1/3..mostly along the frontier...really didn't give a damn, until one party, or the other, bothered them--then they took the opposing side..." It appears to be in our American nature to just be cantankerous and bow-up to authority every once in a while. (Maybe that explains the current Kinky Friedman phenomena???)
Supposedly, the area along the Red River of north eastern Texas was a unionist hot bed...reference the Gainsville hangings. Many of the German settlers in central Texas had come over after the crushing of the European revolutions in the 1840s and having taken a citizen's oath to their new vaderland, felt compelled to be loyal to their national government. In southeast Texas--the Big Thicket country--where large slave holders were not all that common, it was looked on as "..rich man's war, poor man's fight..." There was probably a little of that through out the settled portions of Texas...just as was true of many locations across the south (West Virginia, eastern Tennessee, NW Alabama, Kentucky, etc.)
I cannot find anything concrete...so far...but it appears that my g-grandfather (Jesse K. DuBose, 1st Sgt, Co. K, Bourland's Regt, Border Texas Cavalry, CSA)was involved in hunting down Union sympathizers along with deserters in the Red River/Indian Territory areas. He was in his 40s, with 2 children, a ripe old age for that era, when the war started. There is also a family legend that he, and at least one brother-in-law, (John Hawkins, also of Hunt County) were involved with some of the quashing (a polite way of saying, lynching?) of pro-Unionist before he enlisted with Bourland in 1864.
Some authors (can't recall who, at this point ['old-timers disease?]) indicated that some of the North Texas Union sentiments had spilled across the Indian Territory from the "bloody" Missouri-Kansas border mayhem of the late 1850s.
Sam Houston was practically a son to Andrew Jackson who was his political "sponsor" after the War of 1812. Some think that Jackson was actually grooming Houston to follow him to the White House, until Houston's unfortunate marriage, while Governor of Tennessee, and his almost immediate divorce under mysterous circumstances. Houston then resigned and fled to join his old friends the Cherokees, now removed to Arkansas Territory and (today's) Oklahoma, where his "drinking problems" resulted in his Cherokee name "the Raven" being changed to the Cherokee phrase, "big drunk."
After a while, he sobered up, returned to Washington, apparently received Jackson's blessing to go down to the the Mexican province of Texas and look the situation over. We all know what happened after that. Houston never lost his love and respect for Jackson and harbored Jackson's philosophy of "...the Union, now and forever!..." So, it is no wonder that in a day when politicians still had principles that Houston held firm to his beliefs and refused to violate his oath and service to the United States by taking an oath to the new Confederate government.