I’ve got the OneDrive for Business on Mac synchronising a Team Site by modifying the configuration files. Instructions are here: davidoc.wordpress.com/.../onedrive-for-business-on-mac
It is hopefully just a matter of time until Microsoft updates the GUI to make this more straightforward.
But I’m assuming Microsoft does not officially support this now, so please don’t blame them (or me) if you accidentally delete the contents of a team site!