Nah, doesn't look like it gets called. It's the original implementation, listing the issue which still hasn't been addressed by the similar implementation at https://github.com/christianselig/islandora_importer/blob/75ba2790190f6e474d660b7ced74f9659fac34fe/modules/zip_importer/includes/importer.inc#L238-L250...  Why it was reimplemented instead of just uncommenting the code, I don't know. In any case, we still have undefined behaviour when two datastreams in a DS-COMPOSITE have the same mime-type.