The question is rather old, however in case someone stumbles on it: since January 2013, git has been integrated into TFS (announcement: http://www.visualstudio.com/en-us/news/2013-jan-30-vso#git support). What it means is that the team can now use git as the source control tool (instead of, but not alongside, the "built-in" TFS version control system) while still using the rest of TFS for activities such as continuous integration, issues tracking, and so on.
Original discussion on MSDN: http://blogs.msdn.com/b/visualstudioalm/archive/2013/01/30/getting-started-with-git-in-visual-studio-and-team-foundation-service.aspx
StackOverflow has a large set of relevant discussions (https://stackoverflow.com/search?q=tfs+git), cannot point to anything specific.
