Admin gave the OK two years ago to list these types of cards as long as they're clearly identified as such and not included with the regular base or insert sets. The following is an exact quote:
If the card company purposefully made these as a promo or as a test or as replacements or for some other reason and just didn't distribute them via the normal means, but now they're available in enough quantities that collectors can track them down, put together a full set, they're recognized by card retailers, graded, etc., I think we're limiting ourselves by not including in the database. As long as things are clearly labeled and explained in the release notes, it gives collectors an avenue by which to identify these items that they might encounter out there.
Admin may consider an "Aftermarket" category under Inserts/Related if there are enough examples like Collector's Edge, Fleer, etc.; otherwise everything usually gets listed as an "Insert".