The F4V format is based on the ISO MP4 format, which in turn is based on the Apple QuickTime container format. I haven't found any information about DRM protection in f4v files.

rubbereva.com started supporting Windows Media Player and Real Player only. This should be an indication good enough showing that f4v files (if they use them) have no any DRM protection. Otherwise they wouldn't probably switch to Windows Media thus stopping supporting Mac OS users.

Why do you think think that f4v files on rubbereva.com are DRM protected?