What a quinkie dink...no kidding. I was just in Mexia this weekend geocaching. I was all over that place. Nope, didn't see any compounds with barbed wire, military troops in guard towers.
There was indeed an old German facility for some of Romels corp during WW2. This is true, but no active camp.
Most of the so called FEMA camps listed on the site you provided were military bases. There would be no way to verify.