Good idea if done right.
I had a few construction projects where my crew were DOC inmates. One of them was renovating the Governors house! :O
I have a DOC officer with me most of the time though and the inmates are all illegible for parole in a year or so. They are paid a quarter per hour and their sentence is reduced by the number of hours they work as well. It gives them extra motivation to work on top of being out of their cells. From what I've heard, there was a waiting list...and if any of them misbehave they are easily replaced.