Rather than card counting he was beat counting lol. Card counting in real life isn't exactly illegal, but if you're caught doing it you will be removed from the premises politely and told never to return. The main character might know what a casino is and how the other world might operate one, but obviously in the face of what people can do in this world regular world, the usual tactics and operations simply aren't going to cut it.
Plus it's possible these guys are part of a concerted effort by any of the city's enemies that want to bring the place down (I mean, the city was just hit by a plague of all things.) So maybe escorting them out the door wasn't going to be the easiest thing to do, and would have been boring to watch them try for an entire chapter rather than a chance to show of R'lyeh being kick ass in a fun .5/half chapter.