Lightroom can interpret and apply changes made to photos in Bridge/Adobe Camera Raw/Photoshop (such as the addition of metadata and/or any changes made to color/tone/etc.) and vice versa. In order for this to go smoothly, in Bridge make sure that the Camera Raw Preferences (under the Bridge menu on Mac, the Edit menu on Windows) are set to: Save image settings in: Sidecar “.xmp” files (not the Camera Raw database).
When these “changed/corrected” files are imported into Lightroom, you will not see the changes in the Import dialog box but Lightroom will read the .xmp sidecar file while importing and show you the changes/corrections made to the file in the Grid view. Note: if you are working with the DNG file format, you will see the changes/corrections made to the images in Bridge/Adobe Camera Raw/Photoshop in the Import dialog box.
If you make changes/corrections to images in Bridge/Adobe Camera Raw/Photoshop to files that have already been imported into Lightroom, Lightroom will NOT automatically update the metadata. Instead, a small icon will appear in the upper right corner of the photo cell (in the Grid View in the Library module) warning that the file has changed outside of the application. To update the file either click on the icon and choose “Import Settings from Disk” or select the photo(s) and choose Metadata > Read Metadata from File. Note: sometimes it can take a few moments for the warning icon to appear so if I know that I want Lightroom to read the changes, I simply click Metadata > Read Metadata from File.