I am able to make comments on commits that are made to a branch even though that commit is not part of a pull request, that commit comment is never sent to anyone (not even the committer).

I'm coming from a github to stash migration and miss that ability.

The other nice feature the GitHub > Hipchat integration featured the Stash > Hipchat one doesn't is the ability for the commit comments (or PR comments) to be notified via Hipchat also (right now that's only sent via email if configured).