The issue will be if others are better in AAA, but stuck there because he's "acceptable" enough. I don't particularily like this deal. I also don't know how they plan to score any runs next year, and if you aren't, what is the point of signing a stop gap pitcher?
Do you really see that happening in 2014, though? This season, it's going to be Worley, Deduno, and Diamond fighting for one spot in the rotation. At some point, a pitcher will fail or go down with injury and a second guy will get a shot, probably around the time Gibson is throwing his hat back into the mix.
Next season, Correia is gone. The Twins will (theoretically) have two open rotation spots for Deduno, Worley, Diamond, Gibson, and Meyer. At least two of Deduno, Worley, and Diamond will be gone at that point through trade or ineffectiveness.
I don't see it becoming a problem, really.