@dspnorman-
as of v1.5 of exifixer, it does parse the raw data, i think it might be as simple as creating lookups for the iptc data as well. Might be as simple as returning the $result array and seeing what's in there, especially using an image with IPTC tags in it, so we can get an idea of the raw data.
That's strange. Have you tried entering a title or description in the zenphoto data for the image? If the function can't show IPTC, it will fall back on whatever is stored in the database, so you should not be getting a blank.
It could be that your Canon stores the tags differently than my Nikon, and the IPTC parser in PHP doesn't know how to extract them... I have to confess I have no idea how portable the $iptcTags array is, or if there's a better way of getting at the tag data. I'll try and chase down some documentation on the iptc parser.