They wear hakamas. Other than that, they don't have any Japanese influence. I've always felt Incubi are pretty much evil space elf samurai, tho.
Craftworld Eldar have sashimono banners, power swords that look a lot like katanas, weapons that shoot shurikens, Titans that look like they'd be at home in most super robot anime, and in some of the older fluff there's mentions of Eldar seers sitting in zen gardens writing haiku. They've lost a bit of the Japanese influence since Tau were made, tho, as Tau are supposed to be the manag/anime-inspire faction (primarily the designs; Tau culture is really more of a weird mix between ancient and modern China and the British empire).