I'd consider it, if I knew that Miller wouldn't get hurt and that he'd return to starting after this season. Since I don't know that, I don't want him closing.
Think of it this way: if he does well (has a season much like Jon Papelbon, for example) then I'd be worried that the Indians would be pressured to do much like what the Red Sox have done this spring, and shift him back into the bullpen even after the reason he was going to go into the rotation was because of a health risk.

If he doesn't start off well (and remember: Papelbon was 25 last year) then it'll be just like last year with Fausto. I don't think Miller's confidence will be hurt necessarily, but he'll probably have to go back into AAA and get conditioned for starting again.
Finally, in a worst case scenario, I don't know who else would start if the Indians suffered two injuries to the rotation. I think they still could compete with Carmona/Miller. Jason Davis? Eh.
Speaking of Gammons on BBTN, he was receiving accolades for his preseason pimping of Grady for MVP. Nice.

That's not to say that Papelbon to closer is necessarily a bad idea. But, the teams are in different spots: their middle relief is actually weaker than the Tribe's, I think.