While you can upload music with royalty-free samples from sites such as Splice, Sounds, etc, it will greatly limit the number of libraries willing to represent your work.
Libraries and sync representatives will need an extra step of clearance on Youtube, as that sample, will likely be attributed to another rights holder in Youtube's system. This is called "Multi Clearance" in the library world. It adds another step of manual work for them, adds more legal risks, typically annoys their client, and subsequently - makes the track less desirable than music that doesn't include this extra step.
While That Pitch does work with a select few who specialize in this kind of music, the majority of music libraries prefer tracks that are entirely sample-free.
For best results, we recommend avoiding the use of melodic, harmonic, or looped samples when creating music.
Note: Single shot drum & impact samples are totally fine and won't cause issues! 🙂