According to the MediaWiki.org manual page for generateSitemaps.php, the script has an option named --urlpath (which you should apparently use almost always with the --server option), which allows setting an absolute URL and seems to have been specifically implemented to support Google's requirements for sitemaps.
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According to the MediaWiki.org manual page for generateSitemaps.php, the script has an option named --urlpath (which you should apparently use almost always with the --server) option, which allows setting an absolute URL and apparently has been specifically implemented to support Google's requirements for sitemaps.