Concealed carry was indeed allowed in 2013. In fact, I have pictures (somewhere) showing that the attached hotel downtown (can't remember if it's a Hyatt or a Hilton) had covered up their normally prominent 30.06 signs.
I had some choice thoughts about that at the time, and still do, but I suspect the revenue from the NRA convention will trump any anti-gun sentiment held by the hotel -- at least for a few days.
George R. Brown is city-owned property, and as such a 30.06 isn't truly enforceable.