A lot of these smart meters utilize 802.15.4 (2.4Ghz) radios running a Zigbee stack. 802.15.4 is DSSS like 802.11. The same vulnerabilities exist in both topologies.
There are two pieces to this system. The utility area network and the home area network. They are generally required to be separate bands. For instance, A Zigbee HAN and a cellular backhaul. The architecture of the 'system' would limit a hacker to individual homes. Replay attacks I understand are particularly successful but they don't allow you to propagate back to the utility to shut down entire neighborhoods.
It's just as dangerous as having a wifi router in your home.