Hi Grusha, sorry for the late reply.
Yes, CheckPreloaded will make sure that all the files used in your trials (or only in trials with matching labels if you pass a string) are preloaded before proceeding, regardless of whether the resources live in a ZIP file or are individually fetched on a server. If CheckPreloaded fails to preload all the resources in the allotted time though, it will proceed anyway and any trial whose resources were not preloaded will try to preload them again before starting. But that shouldn’t happen if everything is configured properly.
Let me know if you have any questions.