This is less a theme in it's own right that a way to make zenphoto skin itself to WordPress using the K2 theme. If you wanted to make it work with a different Wordpress theme, just edit the header and footer files to match the theme's leaving the lines just above the </head> tag that deal with zenphoto (should be pretty easy to spot: 1 css link, 1 php function, 1 javascript) intact.
This will work with K2 custom styles as well (although you may need to tweak the zen.css to make it a perfect fit).
download it at my development site and see it at my gallery.