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While that is kind of odd to do, it should not have any effect on your site's search engine rankings or visibility. Simply providing a sitemap file is not going to help or hurt rankings in any way. It will help them discover and crawl pages. That's all. A sitemap file is not required at all, and in fact some sites don't have them--they rely on Google's spiders to crawl their site through the links on their site. The sitemap is only a tool to help them crawl.