tedster - 5:11 pm on May 9, 2011 (gmt 0)
It has always been Google's guideline that the Sitemap URLs should resolve directly and not redirect. This is the first I've heard about notices in Webmaster Tools, but it certainly doesn't surprise me.
When I've worked with moving parts of sites (and I've done a lot of that) we always generate a new Sitemap and verify it before we submit it - as 100% of URLs show a 200 OK response. Sometimes a website has a lot of dynamic churn, and then we test the automatic Sitemap generation to ensure that it doesn't list redirects or 404s, 410s.
I know some webmasters report success by including those non-200 URLs in their Sitemap, but I can definitely report success by NOT doing that. By success, I mean no traffic loss at all in some cases, or only a few day's disruption.
My advice is either don't have an xml Sitemap at all, or submit one that includes only "good" URLs.