Heh. Scyther would probably end up looking like KC's Mantis, yes. As for the Scizor, that's another matter. A Scizor would probably have pincers extending from the forelimb near the wrist that circle around a more human hand. Rather than clinching fully shut, said pincers would probably just serve as weapons alongside the hand structure.
And yes, they would be chitinous, though not over all of their bodies. Unlike true arthropods, Bug-Type Moemon possess an endoskeleton with an exoskeleton-like form of natural armor, especially on the limbs.