Well, I don't know what he means about San Antonio being used as the evac point for the USA, however they are the evacuation point for the Texas coast-especially for hurricane stuff. It is the central hub used for south Texas, for places like Brownsville (though a good portion of their population also goes to Laredo), Corpus Christi, Victoria, and Houston. It is not the sole point where everybody goes, however, it is used as a hub point. When the resources in San Antonio fill up, the people are then routed to other cities such as Laredo, Austin and so on.
I wouldn't expect to hear a whole lot of radio traffic though regarding evacuations because most are face to face. (They are told where to go, and upon arriving to a hub they are further instructed). The only radio traffic you'll hear is on the local jurisdiction radio systems (mostly) wherever things related to the evacuations happen (whether it be an accident, or coordination, and so on).