Maybe it depends what you put in your compost but I'd think that since chickens are omnivorous, scavengers that evolved scratching about in forest litter they would be fine with a compost pile. Forests are full of moulds, bacteria and bugs and many of the fruits would decay before the seeds can be accessed (and part of the ecosystem is birds eating and spreading seeds). Having said that we put coffee grounds in ours which is in a closed bin and I haven't let the chickens scratch over a pile because I'm not sure about the coffee. We do a reverse sort of thing, throw all scraps in the chicken yard then rake it over into a pile each day which they again pick over, then I rake it and put the resulting mess in the compost along with coffee grinds and roost litter once a week. Also, our soil is sandy and poor so I don't really want them picking off the worms.