I am working with Git repositories in the following way:
You could have a look to hg-git GitHub plugin:
adding the ability to push to and pull from a Git server repository from Mercurial.
This means you can collaborate on Git based projects from Mercurial, or use a Git server as a collaboration point for a team with developers using both Git and Mercurial.
Note: I haven't tested that tool with the latest versions of Mercurial.