We are trying to make a connection to SLATE via Microsoft SQL Server and are having issues. Has anyone been successful and can you share your parameters?

This is a pretty generic error, but typically just means that something is blocking your ability to connect to the server. Where is the Slate database located? Can you confirm that there are no firewalls (or other things such as AWS security groups) that are blocking your connectivity? I'd probably suggest eliminating Tableau for now and trying to connect with SQL Server Management Studio--let's get that working first, then see if we can get Tableau working.