You should always use an "order by" clause if you want the results sorted in a particular way.
For DOL tables, the "clustered" index does not put the rows in strict order, it just tries to put rows with similar values as close together as it can without moving any existing rows.
Even with an APL clustered index, ASE could perform the scan using multiple worker processes (if so configured). Each worker process would be returning the rows it processes in index order, but the output streams are randomly mixed together unless an order by clause is used.
-bret