Aside from Rickert bitch-slapping him (amazing), he's essentially untouchable as he is. Ganishka couldn't even stand up in front of him, and all of the arrows the Kushans fired at him had no effect. Zodd's horn being severed was an astral wound given to Zodd in a dream by the "Falcon of Light". So no, Griffith didn't need to be Femto to beat Zodd - the entire scene takes place "between a dream and reality", Griffith is in total control.
I really like that scene though, the Golden Age arc through the Conviction arc is phenomenal.