Google reports they are aware of issues with the indexed URL count in Google Webmaster Tools.
Hear it straight from Google:
Known issue: Sitemaps indexed URL count showing zero indexed URLs
The indexed URL counts for Sitemaps that you have submitted in Webmaster Tools may be showing zero (0) indexed URLs for some sites. We are aware of this issue and are looking into it; you do not need to take any action. This will have no effect on your site’s performance in search results.