This is a regression from 1.5.3 where the behaviour is correct.
If you bundle package --all from a user with git in their path but then bundle install --deployment from a user without git you get the following error:
bundle package --all
bundle install --deployment
Bundler::Source::Git::GitNotInstalledError: You need to install git to be able to use gems from git repositories. For help installing git, please refer to GitHub's tutorial at https://help.github.com/articles/set-up-git
bundle install --deployment should need git if the bundle is packaged.
As noted, 1.5.3 works correctly, this is broken in 1.6.1.
Fixed in #2973