The Raiders signed him after the Packers season ended, when their PS contracts were done. The Packers signed Tramon Williams, Spencer Havner, and their other PS guys to futures contracts at that point, but not Tollefson. Maybe it was Tollefson's choice not to sign with GB, but the Raiders signed him to their off season roster as a FA.
We discussed it at the time here:
http://packerrats.com/showthread.php...off-Packers-PS