You mean the watchdog integrated into the BCM2835? That's a good question, we haven't tested that yet, but I've added it to the todo list now.

One particular product in the Revolution Pi lineup called "Connect" has an additional hardware watchdog which is also capable of resetting attached devices via a relay. That one works even when the BCM2835 has locked up completely. However, the CPU needs to have cooled down a bit to reboot successfully.