Can it mirror exclusively opened and locked files?

Yes, it can mirror any file that is opened exclusively by other application in real-time mirroring (RAID-1) mode only. In fact, real-time mirroring is performed only when a file is opened and being written by the applications. Further, in real-time mirroring mode, MirrorFolder does not even read the source file after initial synchronization, as it duplicates the file I/O request packets in the memory. So, it does not matter if a file is exclusively opened by any other application in real-time mirroring mode.

However, in auto-synchronization mode, the software can copy an open file only if it is not exclusively opened by any other application. So, the file will be copied / mirrored when the application closes the file or you reboot the computer in case the file is exclusively opened by the system itself. So, when setting up a real-time mirror for a folder, make sure that files are not opened in the source folder to complete the initial synchronization successfully.