There is no breather nipple. The crankcase fumes pass the cam followers through the pushrod tubes to the rocker well. There you will find a small passage into the intake port.
http://www.rcuniverse.com/forum/m_5630457/tm.htm
http://www.os-engines.co.jp/english/...ha56/index.htm
The "velocity stack" is a functional piece to improve fuel economy and reduce emissions of raw fuel. I think that the PCV system and carb inlet are things OS is doing to preempt EPA type regulations of model engines.
I think the styling comes from engineers working on multitudes of car engines. Just look at OS production time line. There have been few air engines in recent years, far outnumbered by car engines.