While that certainly should have been a 15 yrd penalty against Klein and not Legate, I don't think that it was overly dirty. Stuff like that happens in games all the time. Gomes' hit on Arnaud was not dirty either. Gomes looked to target Arnaud high, and Arnaud started falling at the same time. It was pretty aggresive, however.
As for Martin's hit, it was a clean football play. He targeted the chest of OSU's player with his shoulder, it was the OSU player who ducked his head which caused the helmet to helmet hit.
The hit which knocked Cody Green out for a couple of plays was the worst of the bunch. From the one time I saw it, the ISU player led with the crown of his helmet, and caused damage to Green.