The central DAM should be configured similar to cloud service configuration (like Marketing Cloud, Brand Portal etc.) at AEM. Then replication sync (on demand or cache) is something consider to get all assets from central DAM to AEM. Then rest of the flow/experience works same since assets are now duplicated and works as local in AEM. But keeping the local copy in sync with central DAM would be a challenge and you can check if that is the use case or not.
Please share the exact use case to talk more on this, especially the lifecycle of assets fetched from central DAM. are they going to be used for Page authoring?
Thanks,
Ashutosh