DreamHost would either configure their FTP server to allow it, or upgrade it if not supported. Apparently the feature to set the timestamp is not standard, just widely supported in recent FTP servers, besides being something that can be turned off.
Also, probably not able to do this using SFTP (SSH), since it is not FTP.
However you can probably put all the images in a tar or zip archive and upload that instead, then use shell to extract the images.
EDIT: ProFTP only supports “read-only” MDTM apparently, AFAIK.
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