I'm not quite sure they would think it that way Zero, or at least publically acknowledge as much.
A possible comment from the Vikings would be to say that "having Brett Favre on the team will give us the best possibility to win". I don't see that as much as an indictment on their current QBs or desperation, but as an act of good faith towards Brett Favre. They can portray themselves as the "saviour", allowing Brett to join a team where he feels competitive and also gives him a chance to stick it to the Packers.
If they succeed and perform well for the season, they can say, 'Brett Favre has demonstrated over this season that he's lost none of his abilities as a future HOF QB'.
If they fail and perform poorly for the season, they can say, 'Brett's had an outstanding career in the NFL, and we feel honoured he chose to play for the Vikings. When you look at a future HOF player who's still capable of playing the game, you have to consider what he could bring to the franchise.'
I don't expect them to throw their hands up and say, 'hey, you got me. We were hoping Favre could win because we certainly can't with Sagvaris Jackenfels.'