Scratch and Peck is great! You just have to make sure they eat the "fines", which contain some vitamins and minerals.
It is a complete feed, just in an unprocessed form. Feed doesn't need to be pelletized to be a complete diet.
Scratch is not healthy. It is very high in fat and should only be fed as a treat, not part of their main diet. Layer feed contains all the nutrients they need to be healthy (though higher protien, around 18%, is better). Treats should make up 10% of their diet or less.