I just bought a bag of cracked corn and noted it to have a large oil stain on the side, and inside the bag was some black chunks. They look fibrous and do not smell bad. Is this something from processing or something bad?
That looks like residue from molasses used to manufacture texturized feeds in the feed mixer. It should not be there, but if it is molasses residue it won't hurt the chickens.
I'd take the bag back to the fee mill and getting a replacement bag.