A Google News Help thread has some reports of publishers reporting that their Google News Sitemaps are reporting "0 Indexed URLs" in Google Webmaster Tools.
I too saw this issue and I thought that perhaps there was a bug in my sitemap file. But Google did not report any issues with my sitemap file, plus, I saw my articles were being indexed within Google News. So I figured, it was a reporting glitch in Google Webmaster Tools. It appears I was right.
Inbal from the Google News team said in a Google News Help thread:
Just a heads-up that the issue with Google News Sitemaps is showing "0 Indexed URLs" is a known issue. This number does not reflect the accurate number of the URLs indexed from your site. The correct number is the number of all the articles you've submitted within your sitemap minus the articles that show News-specific crawl errors under Diagnostics.
I assume this error is being fixed, but there is currently no estimate time for the fix.
Forum discussion at Google News Help.