Have had a quick look into this & from observing ours over the last 2 days I believe that as long as they are free-ranging they'll be ok.
The hens don't seem to be eating much layers - may be a handful or 2 between each flock per day (flocks of 6-8 plus cockeral), though I can't honestly say if the cockerals eat the layers or not. The feeders are hung in their housing, so they have free access to it, they are let-out at about 6am this time of year, later in the winter. They also have a couple of handfuls per flock in the yard, to "call" in the evening.
I guess that chucks, allowed to free-range & forage for themselves know instinctively what they need to balance their diets - certainly better than we do
