As I commented earlier, we had homasote under carpeting in our upstairs bonus room for 25 years. For 5 of those years we had window leaks until I could get the windows replaced. Of course it never rains in southern California! The carpet tack strips held fine, we re carpeted the room once as well. When we took out the homasote in last summer's remodel it was completely undamaged, the nail heads were rusted from the moisture. I think what happens is the carpet and padding absorbs moisture quicker and easier than homasote so unless there is a pipe leak or some major source of water the carpet protects the homasote. The only reason we removed it was it was one and one half inches of homasote with no wood subflooring below it.
I am not recommending homasote for subflooring but based on 25 years of actual experience it worked fine with no issues.
