If would be great if complaints would be moderated before they appear on public. I know that is hard or probably impossible to do, but that separate sub for casino complains will turn into "I got greedy, lost, now accuse casino of not being fair". That is what majority complaints are about. Or, sometimes the problem is so tiny or repeated, that there is no use of making a separate topic. Maybe it is even better to write in casinos ANN topic instead of in separate sub, as casino representatives (OP) not always check forum besides posting in their own topic.
In my opinion Posting complaints or fraud related threads in the Casinos ANN section is ineffective. While it's true that casino representatives don't always monitor the forum except for their own threads in the Casino ANN section, the sheer volume of threads in this section means the complaint or thread will quickly disappear and won't be read by a large number of members.
As you know, dozens or even hundreds of threads and posts are written in this section daily, so the chance of these threads being visible is slim, and only a few will read them.