I just discovered that Sass is missing from my WordPress Development Kit Vagrant box. My Vagrant box is on the latest CentOS 6.5 release and, luckily, setting up Sass is very simple for vanilla CentOS 6.5 users. It is literally a two-step process:
$ sudo yum install rubygems $ sudo gem install sass
Now I can add this to the NetBeans executables configuration by adding the path /usr/bin/sass.
Now I can edit my .scss files and have the corresponding .css files auto-generated right from NetBeans. Nice!