Hi Tim
Yes, APM Server can send data to AWS ES. You will however not be able to use the APM UI in Kibana as that requires the free X-Pack Basic license which it isn't possible to run on AWS ES.
However, the APM Server comes packaged with a few ready-to-use APM Kibana Dashboards that you can use instead. But bear in mind that these dashboards does not provide the same rich functionality as the dedicated APM UI.
To configure AWS Server to send data to a remote Elasticseach instance (as is the case with AWS ES), you need to specify the hostname/port of the AWS ES cluster using the output.elasticsearch.hosts config option.
You can read about how to do that via the command line here:
https://www.elastic.co/guide/en/apm/server/current/setting-up-and-running.html
Or using the configuration file here:
https://www.elastic.co/guide/en/apm/server/current/apm-server-configuration.html
I hope this answers your question 