I'm trying to disable the monitor for a database in a DAG that we don't want to have copies for.

I tried the following, but a few hours later the monitoring alert appears again;

Set-MailboxDatabase Identity "name AutoDagExcludeFromMonitoring $True
Add-GlobalMonitoringOverride -Identity DataProtection\EnableDatabaseMonitoringResponder -ItemType Responder -PropertyName Enabled -PropertyValue 0 -Duration 60.00:00:00

Does anybody know how to disable the database redundancy check for a specific database?

Hi,

According to your post, I understand that you want to disable the monitor for a specific database in a DAG.
If I misunderstand your concern, please do not hesitate to let me know.

Im afraid we cannot disable the database redundancy check for a specific database.
However if you dont want this copy, you can remove this corrupted copy then create a new one:
Remove-MailboxDatabaseCopy -Identity DB1\MBX1 -Confirm:$False

More details about Add a Mailbox Database Copy, for your reference:
https://technet.microsoft.com/en-us/library/dd298080(v=exchg.150).aspx

Thanks