A decent-sized centipede would be able to penetrate the armor, but small centipedes would most likely make easy prey unless they are lucky enough to grip a joint with their venomous bite. A scorpion's sting is generally not aimed at the armor, but directed towards the joints where it's easier to pierce. A scorpion's telson is covered with setae capable of discerning where it is best to try to sting.
The video shows a confrontation between a beetle and a smaller scorpion with only its sting as a reliable defense. An adult emperor scorpion would be capable of using its claws much more effectively to crush prey and attackers than a scorpion such as the one in the video. Notice how once the scorpion's telson is taken out of the picture by a well-aimed bite, all it can do is ineffectively attempt to pinch at the beetle.
It is generally a poor idea to house several predaceous beetles together unless they are known to be communal. I'm unfamiliar with the temperament of Pasimachus, but other beetles such as tiger beetles may only be housed together if kept extremely well-fed. Missing a feeding with tiger beetles would generally result in a severe reduction in how many tiger beetles remain.
