Hello! Yes, they love treats! I like to give my hens the watermelon rinds to pick at, any extra fruit that I don't eat, like extra grapes or an apple or even a banana.
We feed our chickens wild bird seed too as a treat--we just throw some on the ground for them to scratch and peck at. They just love that. They also like dried meal worms.
They love cracked corn too, but it's not very nutritional--it's kind of like candy to a chicken. Chickens LOVE a fresh cob of corn--raw. They will just peck that clean.
I try to stick with the healthy stuff, but chickens will eat just about anything--even leftover dinner--meat, potatoes or noodles. I don't feed mine that.
You have to watch, and don't give them salty stuff like chips or crackers and such. They can get saline poisoning from that kind of stuff. Also, citrus fruits aren't good for them--I guess they're hard for a chicken to digest.
Well, take care and enjoy those hens!