Currently by default if you have the setting checked in the Shared Files Security Settings:
"Filter Invalid Markup and Potentially Dangerous Content From Feeds?"
then NeatHtml is used to protect from the untrusted content and NeatHtml puts a nofollow on all links withing the content. However the heading which links to the original source article does not currently have a rel=nofollow.
I will add a FeedManagerDisplaySetting for the next release so you will be able to use UseNoFollowOnHeadingLinks="true" from theme.skin to force a nofollow there.
Hope that helps,