I assumed they would be unarmed (no ammo is still unarmed in my book) the same way many Guardsmen at the airports on 9-11 were, no ammo. Since their mission is just to observe, I would expect they will have no ammo or even a firearm.
Their main duties will likely be to assist the federal agencies.
Previous call ups of national guard by governor Perry were armed.
More Texas National Guard Called Up to Protect U.S.-Mexico Border
http://www.nationalguard.mil/News/ArticleView/tabid/5563/Article/244/more-texas-national-guard-called-up-to-protect-us-mexico-border.aspx
January 24, 2007
The Guardsmen will form 12 armed security platoons and man traffic crossovers along the Rio Grande River. Each platoon will be accompanied by a Border Patrol agent and a local police officer, according to a release by the governor's office. The Guardsmen are issued weapons, but whether they carry them will depend on the mission, Meehan said.
Last I heard was that they were there to observe and then hand over any illegals to border patrol.
Problem is that once they hand them over to border patrol then the border patrol hand them over to ICE who in turn ships them about the country instead of getting rid of them.
So if that is true then this is all a waste of time.
Still I will wait for more details and hopefully have more responsibility than observe and help with food and diapers.