Can secured OpenDistro ES use unsecured vanilla ES as a remote cluster for Cross Search?

Hi. Quick question: I have a large established vanilla elasticsearch cluster which does not have SSL enabled on its transport interfaces. I have a new empty OpenDistro elasticsearch cluster that I’m evaluating, and it’s using encryption settings on both the transport and http interfaces using the demo certificates. As part of the evaluation, I’m looking to use the OpenDistro cluster as a coordinating cluster, and the vanilla es cluster as the remote cluster in a cross search scenario.
The blocker I’m running into is that it seems I cannot have a secured node on the OpenDistro side establish a remote cluster connection to a node on the unsecured vanilla es side. The error messages seem to indicate that in all cases, both in sniff mode and proxy mode, the secured OpenDistro node cannot establish a connection to the unsecured transport interface (9300) on the vanilla es side - it is attempting to establish a SSL/TLS connection to an unsecured transport interface. It seems to me there’s no way for a secured cluster to connect to an unsecured cluster for the purpose of remote cross search - though I would love to be wrong.

tl;dr, the question is: Is it possible to use an unsecured cluster as a remote end in a cross search scenario, when the coordinating cluster is a secured OpenDistro cluster?

Error message on the unsecured vanilla es side:
[2020-12-02T16:08:28,688][WARN ][o.e.t.TcpTransport ] [use1-logging-hot-1-client-01] exception caught on transport layer [Netty4TcpChannel{localAddress=/, remoteAddress=/}], closing connection
io.netty.handler.codec.DecoderException: invalid internal transport message format, got (16,3,3,1)

The answer is no. Both clusters need to be secured. An unsecured cluster cannot be a remote cluster for a secured cluster.

When using cross cluster search with secured clusters, all clusters must have the Elasticsearch security features enabled.

Enable the Elasticsearch security features on every node in each connected cluster…