I don't know how much Walker or Giddens could have helped or developed through playing last year--or how much they can this year, but I am certain that Doc not playing them and their performance in 2 or 3 minutes of garbage time here or there are poor measures of their capabilities.
They've got to come on strong in summer league, which I'm confident they are both capable of doing, then really know the systems coming into training camp. Even after that, they'll both be lucky if they don't have to wait for someone else's injury for the opportunity to worm their way into the early-season rotation.