I have a relative who does a very specialized job in the IDF and thus has done many tours in Gaza in all phases of the war and in all areas of Gaza.
He describes the tunnel entrances and other evidence of collaboration with Hamas if not direct participation is so widespread it felt to him like אין בית אשר אין שם מת.
Obviously, he's far from the only soldier making such claims, and we have the testimony of hostages about the civilians who imprisoned and tortured them.
Biased as we are, we tend to exaggerate and make our opponent's problems out to be much worse than they are. In this case, I fear we are under estimating the issue