If I'm not mistaken, the index and gallery pages of Zenphoto don't have tags associated with them (which is why they use the tags of all the albums).
You should be able to specify your own tags within the theme's header, however, to achieve the same effect for these two pages. If you still want to include keywords from elsewhere, it would probably be best to create a custom function for your theme using `getMetaKeywords()` from `html_meta_tags` as a template. From there, you can choose what exactly to include on these two pages and how to sort them. As I said before, the relevant line is 223.
From what I've read, most search engines these days will not pay much attention to the meta keywords (Google in particular; Yahoo might still use them). Also, I highly doubt that the order of the keywords would matter, though I have no evidence for this. Chances are that, if keywords are taken into account, then they will be truncated at some point that is determined by the search engine itself.
As a side comment: wouldn't it be better to use `getAllTagsUnique()` instead of `array_keys(getAllTagsCount())` in `html_meta_tags` line 223?