If you submit an XML sitemap to Google, do you have to recreate and resubmit when you create new pages?

Yes, you need to update your sitemap to reflect any changes to your site structure. You can re-submit it automatically by including a reference to the sitemap file (sitting somewhere on your site) in your robots.txt file. This will cause google, as well as other search engines to re-index your site map.

More information about the updating process can be found on the Google support page for this feature.

With most CMS solutions the sitemap updates when you add you content. This is periodically checked by google once you’ve submitted it, so the process should be quite straight forward and automated.