Can I run SQLLDR from my application, for example in a trigger for a form?
If you're using Oracle Forms, this may be possible, but you're asking the wrong guy. If you're talking about a database trigger (as opposed to a Forms trigger), then I would suggest finding an alternate approach. It is probably possible to devise a way to kick off a sqlldr process in a database trigger using something like DBMS_PIPE, but I don't think it is recommended.
Maybe you could create an external table on the fly which would serve the same purpose and would incur less moving parts than kicking off an OS process. External tables were made available in 9i and are well-documented.