What Hal said. Just downloading the videos off of YouTube and putting them in your edit along with HD footage definitely wouldn’t work. They definitely have interesting ideas (my favorite is the R1/ANH interlude with Qui-Gon and Yoda and Vader telling Sidious about the death of Kenobi; those actually feel like real scenes that would happen if the OT was made after the PT) but the videos are very low quality, the exchanges don’t always make the most sense (which is understandable since he’s working with limited voice material) and rely on reusing shots, often over and over again, to varying results. They’re interesting for what they are but aren’t convincing enough to be put in the films themselves.
I do plan on making my own HD versions of my two favorites for my ANH fan-edit myself (Qui-Gon and Yoda and Vader and Sidious; the former because it’ll break up the R1 Vader hallway scene, which I also plan on including, and the opening of the actual film, reminds us that Qui-Gon and Yoda are still relevant, shows that Yoda has been training under Qui-Gon, and it also has some character development for Vader, with the whole “He will never set foot on Tatooine” thing; the latter because it reminds the audience that the Emperor, the Sith and the Jedi are still relevant and shows that Vader has a greater purpose and mission beyond what the original film shows). I wouldn’t be using his videos at all, rather using similar but sometimes different sources, and the scenes won’t be exactly the same (for example, due to some feedback I will at least attempt at an Emperor hologram that looks like his ROTJ self). You could try and recreate some of them in HD as well, but be wary; while you may be able to get away with reusing shots a little bit, it definitely wouldn’t work to the degree NV does it (in which sometimes he is forced to use the same close-up for pretty much all of a character’s lines in a video). I’d recommend if you are to try this, improve the scene itself (remove any awkward nonsensical lines if need be), make sure there’s some time and space between the last time the footage was shown to try and mitigate the familiarity, make it short, and if possible and if you feel it’s worth it, remove the part that the footage actually comes from so it doesn’t repeat.