I didn’t mention it the other day, but I found out that Zero-Project’s music is all free to use in Roblox games (and any other media at that) if the credits are given to the artist.
More info here: License - Frequently asked questions
Because I’ve answered my own questions, this reply will be marked as a solution.
Overall, it seems that Roblox users in the past have inserted soundtracks on the platform that they may not necessarily have owned the rights to use and distribute, so it’s best to confirm with the original artist.