Sorry to add to this confusion, but the following article suggests otherwise.. http://support.apple.com/kb/PH12791.
If you look at the bottom of the article, it says "Some Apple apps, such as Messages and Voice Memos, back up data in iCloud but aren’t included in the list of apps. You can only turn off backup for listed apps."
To sum up, the articles that braden85 links to don't specifically mention voice memos at all (meaning they may or may not be backed up). The article I linked to and quoted above mentions voice memos and that they are indeed backed up to icloud. However, as an extra precaution, I'd backup not only to icloud, but also to your computer.