Yes, it is.
Please keep in mind that it is not mandatory to use a free/open-source license, however you will get extra points if you do.
The reason we made this decision is that the authors of many of last year's were fine with people using their music (and oftentimes other assets too) for stuff like YouTube compilations, but they didn't include a license agreement in their games, which, in most jurisdictions defaults to "All Rights Reserved", therefore making third party usage of it legally unsafe.