Google's advertising says "Watch youtube ad-free". It doesn't say "watch youtube ad-free unless the video you're watching embeds ad content as well", heck it doesn't even say "Watch youtube ad-free*".
So whatever they are actually providing, it's not what they are selling.
As I said in several comments now: My opinion is that if you try to sell me ad-free, sell me an actually ad-free product.
edit: it also occurs to me that the recommender and search engine will not mark nor honor my "ad-free" status, nor will the auto-play feature. So if I pay for ad-free and google says "hey watch this video with lots of paid promotion next", wouldn't that just be google pushing more ads on me even if I supposedly pay for "no ads"?
