The jersey does look to be a genuine 2001 Reebok, the GU patch commemorated the life of Gene Upshaw, who died in 2008 and wore number 63 for the Raiders. He was the executive director of the NFLPA also. That patch should not be there. Also Allen was not drafted until 2004, by the Chiefs and was traded to the Vikings in 2008.
It's been customised to look like Allen's throwback jersey from the 2008 season.