So, like Design75 and Rodg eluded, there are two different sitemaps in question here... The ZC sitemap is much much more about the people and what they see. Search engine sitemaps/sitemapping has a standard that is expected. The ZC sitemap does not "follow" that standard per se as it 1) has a different address location, 2) has different content (formatting for display, other text, etc.), and 3) is not specifically designed for such indexing.
That google doesn't "need" the products, well, true/untrue, what Rodg was eluding to is that pushing the product information is not necessarily going to increase the hits to the site.
Whaat you will find, unless you disable certain options is that the sitemap xml program suggested will in fact provide all of the products. Further, if you are able to setup a cron job, then it can autoupdate at the periodicity you determine.
As to how it works... In a nutshell, that program creates one of the sitemap files that is "standard" for sitemapping. The file references a folder of other sitemaps and the contents of the folder. Each sitemap file meets one of the desired types of sitempa, categories, products, ez-pages, etc... Each of those files is formatted with the information a bot/spider is expecting to find, the information once collected is then used to go look at the data and do it's thing. This type of sitemap is much better than one that say a host creates of all the files on your server... Many of the files in such a sitemap generation are not reachable and serve little to know value to such a search engine...
So hope that helps a little in understanding. Once you have the program installed, take a look at the resulting files and you'll see the difference compared to the people sitemap. :)