Question:
It is possible to connect to an other linux server with samba4 via UCS ad-connector
Answer:
One possibility that could work, is the AD membermode.
Then you join the UCS Server in e.g. an Ubuntu with samba4 installed.
The Ubuntu Server is then the primary domaincontroller, not the UCS.
What is not possible, is the AD connection between the UCS and the other samba4 instance.