Is /usr/bin/etags severely out of date in Yosemite?
Emacs from http://emacsformacosx.com/ comes with a recent etags:

$find /Applications/Emacs.app -name etags\*
/Applications/Emacs.app/Contents/MacOS/bin-i386-10_5/etags
/Applications/Emacs.app/Contents/MacOS/bin-powerpc-10_4/etags
/Applications/Emacs.app/Contents/MacOS/bin-x86_64-10_5/etags
/Applications/Emacs.app/Contents/MacOS/bin-x86_64-10_7/etags
/Applications/Emacs.app/Contents/MacOS/bin-x86_64-10_9/etags
[...]


It's the corresponding version to emacs:

$ /Applications/Emacs.app/Contents/MacOS/bin-x86_64-10_9/etags --version
etags (GNU Emacs 24.4)
Copyright (C) 2014 Free Software Foundation, Inc.