Whole BOSS are absolutely fine for them, the grit in their gizzards will break down the shells for them. Chickens are always suspicious of new things so if your flock doesn't like them unshelled, it might take them some time to accept that these are the same tasty treats as the shelled ones.
I wasn't shelling BOSS for my chickens either, waaay too much crazy work. They will figure it out or their coop will be a wonderful sunflower garden 