I believe Lemon is the simply the result of Randy Meuller's tireless search for any and every QB who can either start for the team or be traded for something worthwhile. That's Mueller's track record -- he once had Aaron Brooks, Marc Bulger, Jeff Blake, and Jake Delhomme on the same roster. The fact that he convinced Saban to give up a 6th rounder for Lemon says that they believe he can be a starter in that mold.
I think Saban views ALL draft picks as being for potential starters, not role players, and I think he uses his late-round picks for diamond-in-the-rough guys like Vickerson and Alabi, who can become starters with good coaching and further development and experience. So that's where Lemon is IMO.