The quote in this page is misleading - you *cannot* edit Camera Data in Photoshop, whether in EXIF or XMP formats, so there is no possible chance of being confused that your Camera Data edits are being stored wrongly.
In all cases where there is non-XMP ("legacy") metadata in a file, such as with IPTC-IRB or EXIF metadata, and if there is an XMP analog of this metadata, the XMP and "legacy" data are kept in sync.
Further, if you were to create an image with EXIF data as well as the XMP equivalent for each field, then you edited the EXIF in a non-XMP-aware app, the next time you open in Photoshop (or other XMP aware app) the XMP will be updated to match the EXIF as it should.
I will clarify this article when I can, but first wanted to put my thoughts in the Talk:EXIF.
PS, I know that quote is from me! I was wrong, or more probably I was slightly confused. I believe I was probably internally thinking about IPTC edits when I talked about EXIF edits, as earlier versions of Photoshop did fail to update legacy IPTC fields and so IPTC and the XMP equivalents could get out of sync. Anyhow, Photoshop does not edit EXIF metadata, it merely mirrors it within XMP packets. If the EXIF is updated (with another tool) Photoshop will updated the XMP record to keep in sync.