You would need to consult the terms of each feed provider to get specifics. I have seen sites that provide full feeds, and yet they were quite strict in terms of syndication of those feeds. Some will say that their feeds are only to be used for personal use.
However, in general I think most feeds are OK to use as long as you maintain the link back to their original article and you don't strip out any information indicating the source of the feed. It's when you try to pass the feed off as your own content that most issues arise.
To be safe I would check the terms of each feed to make sure that there are no restrictions in place.