I didn't see Sakugi, Shimanuki, or Matsuda. But given the lack of sakuga on YouTube, there is hardly anything to see there.
I don't really understand what an animation director means, but I'm sure they are less useful than the animators themselves. At least, I understand what the essence of the work and animators is, and what their finished product looks like
Animation directors basically do touch ups, ie, the correct(redraw parts) of other animators works, while typically also animating themselves. Most animation supervisors tend to focus on just correcting a few key scenes while also potentially submitting their own scene for the episode, while more draconian animation supervisors actually correct pretty much the entire episode to be in their style(a far more difficult feat) and may or may not contribute their own scene.
A good example of a more draconanian animation supervisor back in the day was Katsumi Ishizuka, who pretty much redrew entire episodes(or at least the half of an episode he was in charge of) to look in his style.
I'm not suprised that they don't have many sakuga compilations, though I would have expected one or two for Masahiro Shimanuki in relation to his dragon ball work.
Masahiro Shimanuki was massive name on DB and DBZ, being a strong contender for best animator on that series, probably most notably animating the Kamehameha vs Galick Gun beam struggle in the Saiyan arc. Sadly, he got progressively worse as DBZ went on, his stuff in GT being a lot weaker, and he immediately fell off as soon as joined One Piece(I think his first episode is like episode 5). His stuff in early one piece was serviceable, and arguably was still some of the stronger stuff from the series very very early on, but they were nowhere near the hieghts of his dragonball stuff.
Edit: The job of animation directors is to try and correct or redraw scenes to be on model, or at the very least, visually consistent with the rest of the episode(which typically features their style).
Midori Matsuda is a good animation director(even though she isn't a terribly exceptional animation, because she knows how to draw the characters on model).
EDITEDIT: Even though Shimanuki is the animation director, he tends to get corrected by the chief animation directors(who Matsuda is one of them), whose job is to check all other levels of corrections and add the final touches pretty much.