This is quite questionable. The challenge caches rule 10. speaks about source of criteria and explicitly lists lab cache finds as not acceptable. Given that, I would read that for qualifying for a challenge cache, lab cache finds can not be used. If this is not how the rules are understood by groundspeak, reviewers and in agreement between Project-GC about checkers, they will need to be updated and rules adjusted.
There are more issues with lab caches (such as they have weird timezones and actually might not land in the day you log the cache) and much more, so I believe not including them in checkers is a correct thing.