I clicked on the YouTube link to see if it was monetized or not. It is monetized.
So it's not "is Kirill charging for his music or not?" It's "is Kirill cool with someone else making money off of hosting his music or not?" These are two very different questions. If I was him, I wouldn't be cool with it, but only he can really answer the latter of those questions.
Until then I urge you to visit the YouTube linked in
Kirill's personal website :
"Official" Divinity Original Sin Soundtrack YouTube Video