I am working at Univention in Bremen. Germany.
We are happy to see you compare Univention Corporate Server (UCS) with such a great project like Nethserver. With luck I can help clarifying some things about UCS. I will comment on specific topics below.
Not quite. There is also the UCS Core Edition, which can be use for a small business company, with trained administrator.
The UCS Core Edition provides an unlimited and free License, which differs from the fact, that no support ( email/phone or web form) is included. And you will have to upgrade your system up to the following six months after the release of a new UCS version.
You‘re right. Furthermore UCS provides the function to build up an Active Directory connection with a Windows DC. The Active Directory provides 2 options to configure your UCS system.
The first option is, to configure UCS as part of the Windows AD domain. UCS offers the possibility of expanding an existing Active Directory domain with all the functions of UCS without making changes to the AD domain.
The second option is to synchronize the Active Directory with your UCS domain. This allows both unidirectional and bidirectional synchronization and ensures smooth, parallel operation of Microsoft Windows and UCS environments without considerable administrative efforts. In addition, it is also possible to synchronize multiple Microsoft Windows domains in parallel.
Here some links to the last documentation and other scenarios where UCS focuses on:
I hope it helps with your comparison.