Youtube is very clear on their usage policy;
Music from this library is intended solely for use by you in videos
and other content that you create.
Futhermore, when you download the music from their library. You agree that you will not make it available in any form or anything other than your own creations.
Here is the exact text they use regarding their music library.
Your use of this music library (including the music files in this
library) is subject to the YouTube Terms of Service. Music from this
library is intended solely for use by you in videos and other content
that you create. You may use music files from this library in videos
that you monetize on YouTube.
By downloading music from this library, you agree that you will not:
Make available, distribute or perform the music files from this library separately from videos and other content into which you have
incorporated these music files (e.g., standalone distribution of
these files is not permitted).
Use music files from this library in an illegal manner or in connection with any illegal content.
Additionally, some music files from this library may be subject to
additional requirements as set forth in the library (e.g., attribution
requirements). You agree to comply with such requirements when you use
music from this library.