Yosemite and El Capitan prioritize /usr/local/bin over /usr/bin, so if you install the latest version of git via Homebrew, you're mostly okay. If you're using Mavericks or older, it is as described above.
That said, any program that invokes /usr/bin/git directly instead of /usr/bin/env git would still be vulnerable.
It's not as big of a problem as the article makes it out to be so long as you install a newer version of git.
If you're really concerned, the filesystem restrictions mentioned can be bypassed by booting into safe mode. Though it's still not a good idea to mess with the default program installations since Apple may depend on that particular version of git for some program.
That said, any program that invokes /usr/bin/git directly instead of /usr/bin/env git would still be vulnerable.
It's not as big of a problem as the article makes it out to be so long as you install a newer version of git.
If you're really concerned, the filesystem restrictions mentioned can be bypassed by booting into safe mode. Though it's still not a good idea to mess with the default program installations since Apple may depend on that particular version of git for some program.