Hello,
I would say you are correct in the fact that it is due to it being proprietary and you would be correct that the SDK would be the way to go unless you are looking to also capture user sessions which can only be done by OpenKit.
I do not believe there would be any way to get this into the Service Flow without using the SDK. Thinking about how you might need to approach this as you would not have access to the source code to modify, it sounds like you will need some sort of custom service or proxy which all the traffic to and from the web server goes through at which point you could then use the SDK to capture the traffic. If using a proxy, you might be able to utilize one supported by Dynatrace at which point you would no longer need to use the SDK.
In terms of methods, classes, etc. it's a wide range of possibilities. I would start here on the "OneAgent SDK" page and focus in on the framework language.
References to look at
I hope that helps!
