I'm not sure that will work. The XML that was generated for my site using one of the online generators (I used
XML Sitemaps) includes XML tags like priority and frequency in the XML. I don't think you would get that with a standard RSS feed. The online generator worked fine but it did take between 5 and 10 minutes to crawl my site.
I don't think the Wordpress plugins I have seen offer a great advantage over the online generators. The plugins just automates the process of updating your sitemap whenever the web site is updated, plus the plugins allow finer control to tweak things like priority and frequency.
I was hoping to find something that could generate an XML sitemap quicker than the 5 to 10 minutes the online generator took.