I also found myself needing a hook that runs after new refs are fetched from the remote, no matter if I merged them into a branch or not.

Given the lack of post-fetch hook, I made a python script to simulate it. It works by wrapping the ssh command and call the post-fetch hook after a fetch happens.

Here's the gist: https://gist.github.com/ssimono/f074f40c9ab9efee722e69d1ac255411

Maybe it helps someone.