Yes, I am seeking those units serving in the ANV. However, I am not sure if the ANV existed at First Manassas. Additionally, there were units in the Valley District.
As to POWs, Yes. that is possible. However, since most Texas units remained in the Trans-Mississippi, I wouldn't believe prisoners would have been shipped East. Do you have information on the contrary.
But, you raise a good point, units did serve with the Army of the Tennessee and they could have readily shipped East.
None-the-less, starting with Texas units in Virginia would be helpful in my work.