I have offered walk-ons Scholarships before. Rare in my many seasons, but I have grown partial to one or two. What I have found is that the game will "improve" some potentials once you offer the Scholarship. Some of his reds will turn Orange or Blue and some of his Oranges will turn Blue and Green. It is like the prize at the bottom of a Cereal Box, and you have no control what potentials or even if they will. And yes, I believe once they are scholarship players, you can redshirt if they have not played.