The drivers (essentially, but not entirely duplicate) are in both places because nova-volume is still present in Folsom. It won't be fully deprecated until Grizzly. The OpenStack Project Policy Board (the predecessor to the Foundation's Technical Committee) made the decision that all Cinder drivers included in Folsom would have to have nova-volume equivalents.
Regarding documentation, we'll make the Clustered ONTAP and NFS driver documentation available here on the NetApp Communities site. We're still polishing up final drafts, but expect to have something ready shortly.