Yes you need shims under those springs with aluminum heads, if you don't use them the springs will eat your heads. The reason for stiffer springs for roller cams is due to the roller lifters being a lot heavier than non roller lifters. You need those stronger springs to keep valve float down and to keep those lifters in contact with the cam. If your springs have the correct spring pressure rating required for your cam, use them. Your machine shop most likely tested your spring pressures and that's why they said they were go to go.