Automatically generate standard XML sitemap for WordPress MU, which supports the protocol including Google, Yahoo, Bing, MSN, Ask.com, and others. No
No. The sitemap was defined as sitemap.xml. Your sitemap url should be http://example.com/sitemap.xml
The sitemap is generated when needed. No file created in fact.
You may custom the XML output with feed-sitemap-for-wpmu.php.
Indeed, it should add your sitemap url into your robots.txt automatically, but check your robots.txt by yourself, and add "Sitemap: http://example.com/sitemap.xml" to robots.txt if possible.