Right now entity dumps generated via the maintenance scripts (dumpJson.php/ dumpRdf.php) can only be filtered to either contain all entity types (default) or just a single one (via --entity-type). (Note: For RDF dumps we also have the disabledRdfExportEntityTypes setting, see also T194627).
It should be possible to specify multiple --entity-type arguments, so that all of these entity types are included.