Nuts themselves shouldn't be a problem. Full of energy and good fatty acids that they need. The salt content of various foods we eat can be a problem though. You have to watch that. I forgot and tossed mine a ham bone to pick the remaining meat off. No ill chickens but the waterer was emptied that day.
I should add that my only concern would be if there were any brazil nuts in the mixture. They are so large and chickens can be pigs and choke on things. I say this because my flock members will try to eat a fig whole and I've worried once or twice that I was going to have to perform the chicken version of the heimlich maneuver.