From the docs for DBIx::Class::Schema::Loader:

Currently the loader is limited to working within a single schema (using the database vendors' definition of "schema"). If you have a multi-schema database with inter-schema relationships (which is easy to do in PostgreSQL or DB2 for instance), you only get to automatically load the tables of one schema, and any relationships to tables in other schemas will be silently ignored.

At some point in the future, an intelligent way around this might be devised, probably by allowing the db_schema option to be an arrayref of schemas to load.

In "normal" DBIx::Class::Schema usage, manually-defined source classes and relationships have no problems crossing vendor schemas.

So it can be done, but not by DBIx::Class::Schema::Loader, and therefore not automatically.