Its running Linux, and its using EXT4 for internal storage, a common native Linux disk format, so it really doesn't need to be defragmented. Linux allocates data differently than Windows does, in contiguous blocks, and so its not nearly as prone to fragmentation as a result. Why Microsoft has never addressed this issue, as nearly every other operating system and file system format has, is anyone's guess. But defragging isn't really anything you need to worry about with EXT4.
Not that I am aware of, but it is probably possible to enable ssh and log into the drive using a terminal.. From there, you can most likely run apt-get and install a defrag tool that can run thru the same command line.. If it is anything like the MyBook Live (most likely is) then the ssh name is "root" and the password "welc0me" (that is a zero "0", not a capital o "O").. My guess is it's running a form of Debian Linux, so look for defrag tools compatible with Debian..