Does Oracle's "date'[yyyy-mm-dd]'" literal always use the yyyy-mm-dd pattern?
It is not function, but date literal. And, Yes, it always matches YYYY-MM-DD regardless any oracle settings.
Here is a link to Oracle 10g SQL reference, on datetime literals. Excerpt:
The ANSI date literal contains no time portion, and must be specified in exactly this format
('YYYY-MM-DD'). Alternatively you can specify an Oracle date value, as in the following example:
TO_DATE('98-DEC-25 17:30','YY-MON-DD HH24:MI')