First, it's prison. So, y'know, punishment on some level. In addition to rehabilitation. So my gut reaction is that I'd rather see more educational programs going on. Especially since a lot of "entrepreneurship" is really just either scammy behavior or flat-out fantasy (my start-up's the next Facebook!). Especially when the education isn't in place.
That said, I'm not entirely opposed to the idea. But, as a tax-payer, the idea that someone is getting free room and board on my dime while they make a good income grates a bit. What does it cost to keep someone incarcerated for a year these days? $40k? If the inmate were to repay this -- the sort of rent and bills every other entrepreneur has to pay -- then the idea would be more palatable.