I am not sure the doc is up to date and that you can use an engine from the launcher.
I would download the full engine from github and rebuild the DatasmithSDK program so you get the lib and dll.
Why do you need the Datasmith SDK? Are you making your own custom datasmith exporter?
I downloaded the engine from github. Are you saying all I have to do is build the engine and the lib and DLL files will appear inside Engine\Binaries\Win64\DatasmithSDK?