Thanks @Yuya already took a look on this and will give it a try with a smaller customer. But that's not the point I'm asking for.
Even though in this case I would miss Merakis statement if we'll be able to import users from Business Manager, so they can authenticate against SM and will show up in owners so I'm able to use the owners mail to set up his account on his device.
After going through this feature (you linked) with an Apple technician I can confirm, that this integration makes only sense if you have BYOD enrollment scenarios for User Enrollment. This will give your organization the ability to prevent your employees to use their company mail as a private Apple ID for purchasing Apps etc.