Yes you can do this with any file replication tool, but synctoy and robocopy will not support http paths to files - retrieve the UNC path to your library in sharepoint by opening the library in windows explorer from the actions menu: -
http://sharepoint.site.com/sites/sub_site/folder/document_library/document_folder will open up in explorer, this converts into the following UNC: -
\\sharepoint.site.com\davwwwroot\sites\sub_site\folder\document_library\document_folder
Test the above in explorer again to make sure you can browse to it and use this when setting up the location in your replication tool