There have not been many.
2000-2012 Receptions by Listed DBs
The chart shows defensive backs with more than one reception since 2001, according to ESPN Stats & Information.
Mike Furrey, who spent three seasons with the St. Louis Rams, leads the way with 221 receptions. I thought of Furrey primarily as a receiver, but he did play safety as well.
Rashied Davis, who converted to receiver after entering the NFL as a cornerback, ranks second with 92 receptions.
Peterson is next with a mere four receptions.
The numbers in the chart suggest we should remain skeptical about any defensive back making significant contributions as a receiver, particularly when the player remains a core player on defense, which Peterson obviously is going to be.
Peterson is a special athlete. How much he contributes will hinge on how much the Cardinals need him and how well Peterson fares when given opportunities.
The staff in Arizona does appear serious about giving Peterson a chance. That's a start.