The Portal content directory can be on the file system or in S3 buckets or Azure BLOBs, the latter two which would fall into object storage category.
Server directories can only be on the file system but the Server config-store can be in DynamoDB or Azure tables.
Finally, the ArcGIS Data Store directories must be on the file system.
So in short, yes, but it depends on the product and only S3 or Azure BLOBs are supported.
