I can answer this from personal experience. Birds should not have corn cob bedding. Corn cob bedding gets wet and can grow a fungus that causes a disease called aspergillosis. This is really deadly to birds.
Now I have to say that I don't know what its effects on chickens would be but I can tell you that people lose parrots to this every single day. Its a very devastating disease.
I've been told my several veterinarians that NO bird should ever have corn cob bedding used near them.
That being said, aspergillosis can be found in all kinds of environments but for some reason corn cob bedding seems to be the worse offender.
I'm knowledgable about this because I have here in my home 2 parrots that almost lost their lives from aspergillosis. Neither of these were my birds but birds that we given to me after they got this devastating disease. It took lengthy treatments, costly medication to get these two back to health.
I know that some will say "they're only chickens" but aspergillosis is a horrible way to die. Please find another suitable bedding.
Laurie