I also use xml-sitemaps.com.
About 1 week after submitting my sitemap, Google Analytics said that there was 1 linkerror, because it was a re-direction url.
But I decided NOT to do anything about it, and the next day there weren't any errors at all.
So I guess, Google has a some kind of built-in analyzing filter, that will give a warning at first, but will then give 'the green light' after a second investigation.
Just my thoughts...