Sure, that's also possible.
But I'm using this in an ESXi shell, so ESXi can stay up and running, and only the VM that you want to copy needs to be powered off.
Originally I was just backing up the ESXi system partitions this way - I described that in my blog post here: http://www.v-front.de/2012/09/the-sbhvl-project-part-2-backup-and.html -, and later I modified the script to also backup VM files with tar.