There is no general problem when it comes to including lab caches in checkers, but the checker author needs to make sure that they are included separately. Since lab caches are a separate system, they need to be handled separately. Many checkers were written before the information about lab caches was available to Project-GC at all and it's quite probably so that a number of checker authors haven't updated their checkers since. It is, however, possible and there are checkers that do include lab finds (like the normal calendar checker, for instance).
Also note, however, that lab caches don't have all the information that normal caches have and even some of the information that they do appear to have isn't available to Project-GC. This includes the coordinates, so lab cache finds are in effect locationless. That won't make any difference for this particular challenge, but for a challenge that requires the finds to be in a specific country or other area, lab cache finds can't count since they don't have a location that Project-GC can access.