It's not a default one, name is HiQDock. Though, it's not very usable. As there's no transparency supported, it takes screenshot of a background, so it might cause graphical glitches. The default dock (see the screen with Cave Story) is much better, works perfect
This is not possible. Corners were done with ags. Actually, now the whole bar is ags, I don't use waybar anymore. But the design is the same