It seems that when we edit photo metadata on OneDrive synced files on the PC using Windows File Expolorer, that the entire image is then transmitted to the OneDrive cloud storage. I believe that the Windows Server DFSR file replication uses a differencing technology such that only the difference between the files needs to be transmitted.
Currently it seems that any tags added to OneDrive online photos using the Internet Explorer are not actually inserted into the metadata of the image. Using the DFSR technology might make it easier to go ahead and edit the file metadata, so that the tags added online are also available when searching on the local PC.