There have been so few pitchers - maybe less than3 per season on average - who come over Asia that evaluating the imports is hampered by the small sample size.
That said, the Asian import relief pitchers have had numerous success stories, like Koji Uehara, Kasahiro Sasaki, Taki Saito, Shigetoshi Hasegawa, and Hideki Okajami, and probably a few others...