It shouldn't take much to add to a pistol, for instance, to make it unrecognizable to this. In fact, I'd be very surprised if it works well with small handguns today like the Ruger LCP or the Kel-Tec P-3AT.
I beg to differ after examination of the details of the shooting here and the other places he scouted before it. Catching weapons in general is good for any property, but the purpose is particularly to prevent something large scale (the Westgate property in TFA is next door to the LV Convention Center, and at it's busiest will have many crowds coming and going at the beginning and end of each expo day).
I don't know if this tech is the answer. I suspect paying qualified people to do this type of surveillance with video would be more reliable (I've read places like Israel have been doing it for decades), but casinos won't pay up.