What percentage of the free population 422,000 of Texas in 1860 was Hispanic? I can't find hard numbers. We know 2,500 served in the Confederacy, and we find ample evidence several hundred served in the Union army. My point is that i have a suspicion that between the several hundred Hispanics in blue and the 2500 in Gray, we may well have accounted for a large portion of men of military age in the Tejano community in Texas. But I readily admit I don't have hard figures to back that up.
If anyone reading this is Hispanic, I would not wish to risk offense, because the grievances Tejanos experienced in the years between 1836 and 1861 (and actually far beyond it) are not insignificant burdens. But the issue at hand is about the OP's question. Would those Tejanos who were angry enough to join the Union tilt the balance had Lincoln tried to prop up Sam Houston, and I do not believe their numbers high enough, to have tilted the scale.
I welcome research that shows Tejano active support for the union to exceed their support for the Confederacy.