By default Visual Studio can handle multiple git repositories in one workspace. But if the repositories are in subdirectories this will only work after a small fix.
When the FreeBSD project switched to git for the ports development I had several days the problem that portsnap didn’t allow me to update the ports tree. I searched for a solution to get an up-to-date portstree. One solution would be to use the git repository directly. How I used portsnap to update the ports tree regularly Every night at 3:00 I ran a cronjob which fetches the current snapshot of the port tree.