Yes Amazon S3 API compatible (may be something might be missing)
As explained in earlier post iSCSI is a low level protocol sending SCSI commands over TCP/IP.
Ceph is a higher level distributed file system (it does not work directly with scsi controller or disk or ssd).
So there is in essence nothing common between iSCSI and Ceph except you can mount iSCSI target and Ceph using the same mount command in OS, for windows you can install an iSCSI driver and mount the iSCSI target, not sure how will you mount Ceph in windows machine (never tried it, as in my team no one touched windows and related os for over 6 years, except for using browser to test apps).