When you actually launch the SCORM you're taken to "mod/scorm/player.php" and on line 193 of that it says
$PAGE->requires->css('/mod/scorm/styles.css')
You're right, it looks like a bug in the SCORM module, they've hardcoded a link to their style sheet:
So not only can't you opt out of that file, it won't be compiled and compressed with the other CSS that Moodle uses -- edit: actually it will as it's output twice, once in the compiled and compressed CSS, and once again on it's own.
(And while I'm on the subject, why is the original CSS layed out in a more compact for than the big CSS file. I would have assumed, if it it touched it at all then it would be compressing it, but it seems to be adding line endings semi-randomly, presumably to make it look nicer?)
Yes, with your hint I took a second look at the code and got this to work:
$THEME->plugins_exclude_sheets = array('mod' => array('scorm'));
so if the CSS file is referenced as mod_book, or block_community you need to split on the first under_score. I'm all excited to go and see what Moodle looks like with no plugin CSS now.