As far as I'm aware, currently only DC simple elements will appear in AtoM when included as metadata in an Archivematica AIP. There is a basic mapping in the Archivematica documentation here, which I believe would also apply to object metadata added to a metadata.csv file:
For more information and recommendations on metadata in Archivematica, I would suggest starting a thread in the Archivematica forum.
However, looking at the DCMI documentation, I think the DC Identifier
would fit your needs:
Definition: An unambiguous reference to the resource within a given context.
Comment: Recommended practice is to identify the resource by means of a string conforming to an identification system. Examples include International Standard Book Number (ISBN), Digital Object Identifier (DOI), and Uniform Resource Name (URN). Persistent identifiers should be provided as HTTP URIs.
This will display in all AtoM templates as the identifier following import.