Is it a parody as understood by the law, though? How is it parodying Jay-Z? It's definitely "for fun", but it's not clear that it's making fun of or commenting on Jay-Z.
It's really not clear to me. This page cites a case where someone imitated Dr Seuss' literary voice and lost.
This is the point I was going to make. For a parody fair-use defence to be valid, you need to be parodying the thing you are infringing on, and as much as people always say "oh this is parody so it's clear fair use" by the accounts I've seen (such as Penny Arcade's Strawberry Shortcake comic) that can be a difficult defence to actually mount.
The author even says that he didn't pick the texts to comment on the voice in particular, but that doing the same text (the copypasta, the Bible, etc) with each voice was just convenient.
It's one thing to impersonate someone to make fun of them, but he's not picking texts for them that way. A Bush impersonator reading the phone book isn't obviously parodying Bush unless he starts throwing in comedy Bushisms or exaggerating the voice for effect. Some Elvis impersonators are parodying Elvis but a lot are just doing a straight recapitulation of his look and voice.
No. The video in question was not. And more generally just because an ad plays along side a video does not mean the video itself is a commercial work, in the same way a newspaper or magazine can have ads alongside editorial content.
1. It's parody. Parody has specific statutory protection.
2. It's clearly labelled as speech synthesis.
3. It doesn't stand in for any of the original works. The market for deep fakes is much different than that for songs or presidential speeches.