Whether or not he is forgiven isn't the issue at all. And if forgiveness was the issue, it is not our forgiveness that matters here. It's the people in the NFL writing the checks but any idiot knows that compassion and morality are not currencies they deal in.
That said, people from all walks of life and across all vocations commit crimes, go to jail, and upon their release resume said vocations. There are obvious exceptions though. Say a Dr. does jailtime for gross neglegence, his license to practice will be revoked. If a crane operator get's loaded and kills a bunch of people he ain't gonna get a permit to operate a crane anytime soon. If a defense attorney is convicted of taking bribes from the prosection then he'll lose his license to practice. You could go on forever with examples like this. These are all positions that are some sort of public service and said crimes were committed while carrying out that public service, so in cases like this it makes obvious sense that those people should not be allowed to practice those professions.
Vick's crimes had nothing do with football, they had nothing to do with the integrity of the profession (and when i say integrity of football I mean his actions did not effect the outcome of games).
I don't like it anymore than the next guy. He's a dirtbag and I would not want him on my team. But I don't see any compelling reason that he shouldn't be allowed to play if someone is willing to pay him to do it. He's paid his debt to society. In no way am i commenting on whether or not that debt was just or not, but it's been paid.