We want to ensure that all data that arrives at Forwarder 1 is successfully received by Forwarder 2.
If we enable Indexer Acknowledgement, will Forwarder 2 send acknowledgements as soon as it has sent the data to the non-Splunk receiver? Or is this only possible if Forwarder 2 is sending data to a Splunk Enterprise Indexer?
According to the document you linked, if there is no acknowledgement coming from the non-Splunk receiver to Forwarder 2, then the Acknowledgement from Forwarder 2 to Forwarder 1 is only around that part of the chain. So Forwarder 2 will acknowledge receipt of data from Forwarder 1, but that does not guarantee that the data was successfully sent to the non-splunk destination.