Yes I fed mine old fashioned oats as well. Never gave them boiled egg but I bet they would love it. If you feed them very much I would give them some chick grit just to be safe and have no crop problems.
I feel that plain live culture yogurt in small quantities is ideal, as it gives them good gut flora. You may have to mix it with something to get them eating; the starter is fine. But you can probably give them most anything on the treat chart. Just be sure the quantity is small so they are mostly eating starter. Here is a link to the treat chart, in case you haven't seen it: https://www.backyardchickens.com/web/viewblog.php?id=2593-Treats_Chart
