Using VRTK as a submodule works just fine! Steps:
Set up symlinks for git on Windows:
To allow symlinks you need to use Windows Vista or later, have admin rights or a specific privilege and use NTFS: https://github.com/git-for-windows/git/wiki/Symbolic-Links Install the latest git via https://git-scm.com/downloads and make sure to use the installer. Make sure to at least use "Use Git from the Windows Command Prompt" and at the last step make sure to tick the checkbox "Enable symbolic links".