1.
If a cluster is running in different Active Directories: Can the sync user be managed only on an AD level (not local accounts?
Also it should be considered that a Active Directorie trust is not possible!
Is there a way to use two different Active Directories but with the same user account names? ( there is no need to manage two AD)
2.
Can a DMA connect to two different AD (this AD's don't have a trust!)
It's currently not possible for one DMA to use multiple Active Directories (without setting up trust between the domains). You could have DMA 1 use AD 1 and DMA 2 use AD 2, but then you can only login with users from AD 1 on DMA 1. This may give problems if the account names are in fact identical though.
You may be able to achieve what you want by enabling SAML or RADIUS authentication in DataMiner.