To be honest there have been spells during the last season or two where he's been fit and ready. Moyes hasn't used him though, simply because we've had fitter, better options.
I think more than anything Vaughan needs continuous games, the more he plays, the fitter and stronger he'll get. For us it's just a case of play the odd reserve game here and there, train and train even more.
I'll trust Moyes' judgment on this one, he knows there's a player there and sending him out on loan, giving him the best possible chance is the way forward.