IMO any flock that contains anything besides mature laying hens should be on a flock ration. The protein and calcium levels in layer really aren't correct for roosters, ducks, non-laying or low production hens, young birds, etc. The best thing to feed any flock is really a good quality grower/raiser. The extra protein isn't ever gonna hurt anybody and is usually quite beneficial, and there's no way for a bird who doesn't lay or isn't currently in production to consume too much calcium because she's controlling her own levels with oyster shell.
A good quality feed should contain all the vitamins they need, but a bit of supplementation isn't gonna hurt them. I use NutriDrench as a pick me up in sickly birds. I have way too many birds to give it to the whole flock on a regular basis, but I'm sure it would be plenty good for them every so often.