I believe that all baby sheets need to conform to standards, but that there are ways for them to conform without being introduced to chemicals. A call to PBK readily revealed that none of their sheets are treated with chemicals. Coyuchi, an organic bedding company, sadly told me they needed to call me back. I haven't received a call yet.
From what I can tell though, consumers don't need to be told that their stuff has been treated.
Danielle, Nick, Gigi ('08) and William ('11)