What is Watchdog
Watchdog reboots the Apple TV it if the GUI isn't running.
Apparently BackRow.framework does "BRSettingsHelper tellWatchdogWeAreUpAndRunning"
How to disable Watchdog
This Apple document about Watchdog may shed some light:
http://docs.info.apple.com/article.html?artnum=106588&coll=cp (However, on the Apple TV, there is no /etc/watchdog.conf, other than what this document is saying)
Watchdog is not used in Mac OS X 10.4: look at launchd.