ArchivesSpace actually has a very hands-off approach to data. ArchivesSpace is a tool used to describe the intellectual assets of an archive. Archival description tends to take a somewhat high-level view of the materials in an archive, usually at the shelf, box, and folder level. For particularly noteworthy material, archivists may describe a particular page or group of pages in a folder, and provide access to a digital surrogate of that material.
ArchivesSpace has levels of description at all of these levels. Bundled together, these descriptions are typically called "finding aids" (e.g. an aid for finding the material that is in the archives from a particular donor). For example, this is a finding aid on the demo site for "Jedediah Horcrux Congreave fly fishing correspondence and photographs":
http://demo.archivesspace.org:8081/repositories/2/resources/1
If you scroll to the components of the finding aid and click on "Correspondence":
http://demo.archivesspace.org:8081/repositories/2/archival_objects/1
... then "1925-1935":
http://demo.archivesspace.org:8081/repositories/2/archival_objects/3
... you'll get to a filefolder-level description for some letters that contain illustrations. In this demo, there is one digital object instance for one of the illustrations for one of the letters:
http://demo.archivesspace.org:8081/repositories/2/digital_objects/1
This is the digital surrogate level. One of the key design decisions of ArchivesSpace, though, is to not include digital asset management functionality in the application; these digital assets are stored and managed outside of ArchivesSpace. What is in the digital object record within ArchivesSpace is a URL pointer to the digital object. In this example, if you view the source of the page you'll see the image itself is on a separate server:
http://www.archivesspace.org/demos/Congreave%20E-1/ms292_001.jpg
So any integration of file storage with ArchivesSpace happens at this URL level. The ArchivesSpace application has a published RESTful API that other applications can use to create/read/update/delete data. In the use case you are describing, a combination of the REST API calls (https://archivesspace.github.io/archivesspace/doc/file.ARCHITECTURE.html) for digital objects would allow an external application to push data into ArchivesSpace.