I find enough dust at the end of a container of pellets or flake that I've never found it necessary to grind any, but I don't see there being any harm.
What kind of chickens do you have that require grinding chicken feed smaller?
As for the veggies, sure you can, but often it needs to be blanched, and IIRC peas are commonly de-shelled. I feed excess romaine from the garden when in season, but I don't go out of my way to purchase it otherwise since I feed a spirulina-based flake to nearly everything I keep. (For lettuce no blanching is necessary and magnetic algae scrapers work great to clip it to the side of the tank - my fish don't seem to eat from a big piece if it's just floating about.)