Is it possible to move the themes folder above the root?
I am using MSM and want to move the folder away from the main site.
How would that make sense? For EE to function, it needs a resolvable URI to access the contents of that file. If you don't have an accessible folder for this setting:
URL to your "themes" folder
Your site won't function. Technically, if you're on Linux, you might be able to move it above root, but have a symlink to the folder path. I can only imagine that you have FTP users who's home is the web root, and you don't want them messing with the themes folder.
ln -s /path/to/new/themes_location /var/www/html/themes