Hello,
as far as I know, the various download servlets, CMIS API and some specific ReST APIs support ranged content retrieval. I haven't checked the WebDAV implementation yet, but I would expect it to support ranged requests too.
The method by which these APIs support it may differ. Download servlets definitely use standard HTTP Range header, CMIS API uses method defined for the specific binding you use.
Regards
Axel