Sounds like they're more or less the Jiangshi of chinese myth (really, what else could they have been?). Jiangshi feed on chi, or raw life force. I've seen them do this in fiction usually through draining breath. They may be rotting corpses, are too stiffened with rigor mortis to move in any way other than hopping around, and may or may not be mindless predators.
Now obviously there's gonna be some difference in how they operate in the Dresden Files. Maybe as time goes by and they absorb enough chi, they become sapient and regain a degree of mobility. That might also partially explain why they never leave the Yangtze River valley; they just can't get around all that well, and they've had thousands of years to get their homes just so.
