Mine have been getting red grapes cut into halves and quarters with a scoop of plain yogurt for weeks now. Have given blueberries a few times too but they like grapes better.
Mine turn into Olympic jumpers when the blueberries are ripening, LOL. When I had a poor RIR hen dying, the only thing that perked her up was to tell her I had blueberries and it was the last thing she ate before she died. They love them.
Frozen grape halves are some of my girls favorite things. Frozen mixed veggies are another favorite around here too. I guess if you live in cold country it would not be so wonderful but here were it gets well over 100* in the summer almost everyday, it is a welcome treat for them to get frozen goodies.
You bet they can, I don't cut them up it is so much more fun to watch them play catch me and my prize if you can. it also helps with boredom to give them something to do.