the error message mentioned in your first post about not being able to ssh into the DC is a dead giveaway for a rather common error case: the UCS installation thinks that the DC is another UCS system and not a Windows system. It therefore tries to join a UCS domain as a UCS DC Backup.
This usually happens if, during installation, you configure a DNS server that doesn't resolve the appropriate records properly. What UCS does is similar to what a Windows server does when you tell it to join a domain: it tries to retrieve a special DNS record that tells the UCS system the name of the AD DC.
The most reliable way to fix this is to re-install UCS. Right at the beginning a boot menu with three options is shown. Select the second option (the one with "manual network configuration" or something similar). Then during network configuration make sure to enter the address of one of your Windows AD DCs as the DNS server to use for UCS.
That way UCS should realize the domain you're trying to join it to is a Windows domain. Later during the installation process UCS should then offer to join the server as a member server in a Windows domain.
Note that a UCS system does not support AD DC operations together with a Windows-based AD DC! The underlying Samba software does, but UCS itself doesn't. You can run UCS as a (non-DC) member with Windows-based AD DCs, though.