Is the yellow claptrap in arid badlands an easter egg or something else?
It's possible to get up there, but it's a tricky place to get to:
As far as I know, it's just an easter egg - there's nothing much that this Claptrap does. Someone on the YouTube video said that you get XP for saying there a while; I never noticed this on my playthrough. He is decorated with Gearbox colors, for what that's worth :)