You know... I think I know the perfect job for Moria. It would be like a dream job for him. He could be based out of Impel Down. Whenever new prisoners arrive, as part of their baptism, they get their shadows taken. He would get a continuous source of new shadows, some of which would be very strong. As for zombie bodies, there are deaths all the time in ID and the Whitebeard war may generate some high quality ones.
On the World Government's side of this equation, no one would
ever escape ID again. Even if someone got out of the prison, the moment the sunlight hits them they would die.
The only negative from Moria's point of view would be he would be anchored in one spot. I suppose he could run away from his post though once his army was big enough.