Configuring the Response From did the trick to get ACKs, and NACKs from the Business Operation to original sender.
The second part was to NACK based on un-routed messages. Is this possible?

I see in RoutingRule [ruleSet, rule, when] I can add a otherwise and a transformationDTL into a NACK to target back to the Business Service.

Will this work?

I am doing this with a routing rule.

When working with Ensemble, with Ack Mode set to Application on the Business Service, it is supposed to respond with the ACK acquired from the Business Operations.

This is not happening. Is this a bug?