I did a forum and trac search and it seems no one made one now so I made one that is based on Tris' latest comments function from the zenphoto admin.php.
Place the file as rss-comments-php within the zenphoto root directory. The link for the theme files then is simplye "rss-comments.php".
Here is the code:
`
en-us
http://blogs.law.harvard.edu/tech/rss
Acrylian's ZenPhoto Comment RSS Generator based on Tris's Latest Comments function from zenphoto admin.php
`