The argument given against D&D seems to make it clear that the person making it has never actually played or researched the game, which seems a bit unprofessional to me.
As for whether or not prisoners "deserve" D&D, that question cannot be answered until the government can be bothered to concretely establish what our prison system is supposed to be FOR.
If we only want to keep criminals away from non-criminals, then I see no reason why they should not have D&D.
If the intent is to punish them, then they should never have been allowed things like games or religion to begin with and I don't see why they aren't being tortured as we speak.
If the intent is to reform them, then this is a question for a criminal psychologist who understands D&D.
In the first to cases, execution and subsequent cremation would seem far more efficient from a financial standpoint (depending, of course, what priority we place on not killing the potentially innocent).
I, personally, see no reason why prisoners should not enjoy themselves if it isn't hurting anyone else as I do not feel qualified to pass judgment on the morality of another person and prefer to examine matters from a purely practical standpoint.