Managed is not a tag, its another field, one that Yep uses to mark documents as 'something I want to keep track of'.
If the path is a directory, it will likely apply tags to the folder, not the files inside. Leap can apply tags to lots of documents at once. I agree that it would be nice to have in a command line tool.
With tagging being built in to Mavericks, I think that there will be many more uses for tags in workflow solutions in print, etc. This will mean that command line tools will become more popular.
--Tom