Sorry for dropping the ball on this topic - I got busy and forgot about it.
If you're using the ApmServer kind, you don't need to configure the APM integration. The APM integration is only needed if you intend to run APM Server with Elastic Agent. When you're using the ApmServer kind, ECK is setting up the apm-server binary similar to what's shown in APM Server binary | APM User Guide [8.9] | Elastic
Let's keep discussing over in How to get ECK APM to work with any type of agent at all!?! - #8 by axw