It's not who he signed it's the fact he didn't have another option on the roster this late in the season. At one point under Angelo and Lovie the Bears had Hester, Danieal Manning, and if need be Bernard Berrian Earl Bennett or Rashied Davis to pick up the return slack. There was depth at the position no not all of them were Hester but he didn't have to sign a guy off the street.
There should be someone on the roster that has the ability to step in if necessary. Someone that's been practicing with the team each week throughout the season, someone you know for certain is in football shape and knows the team workout/study routines. someone that's been in the film room with DeCammelis someone that knows tendencies of the blockers etc.