How can I apply tags in Mavericks recursively?
There's a CLI tag tool available via Macports/Homebrew: https://github.com/jdberry/tag

It doesn't seem to have a recursion option, however, I would imagine you could use this in conjunction with the standard UNIX 'find'. 

e.g.,
(from inside the directory you want to tag files in)

find . -exec tag --add tagname {} \;  -print