The State National Guards receive most of their operating budgets & equipment from the US Federal government. There are also statutory requirements that State Guards comply with all Federal military regulations. So it's Federal money Texas is denying when they block same-sex benefits, not State.
For instance, all Texas National Guard Officers must be dual-commissioned, holding a qualified commission in the US Reserve from the President, as well their State Guard commission from the Governor. This is known as "Federal Recognition", to prevent the Governor from appointing unqualified "Kentucky Colonels". If a Guard Officer doesn't hold a US Reserve Commission then they can't receive any pay, and have no authority over other uniformed military.
Additionally, States must be in compliance with published US military regulations, and with which their own State regulations must not conflict. Furthermore, those Texas National Guardsmen activated on Federal service, for instance serving in Afghanistan, are governed solely by US Regulations and policies, not State.
So that this is indeed petty obstructionism by Texas. And if they persist, I hope President Obama exercises his authority to cut off their National Guard funding, and seize their equipment, turning them into nothing more than a ceremonial militia, a glorified version of the State Police.