i connected a pressure Gauge to the Crankcase nipple on my .72 GK Saito engine today, was curious about it and it does fluctuate. sucks and blows. turning it over buy hand the needle would go to negative pressure vaccum and then to Positive pressure. So connecting it to the muffler i would think is a bad idea. The muffler would be pressurizing the crank case and may blow seals out in the engine.
Now if you want a PCV Valve like on a car and your inventive and want to burn that excess oil you would Connect it to the intake manifold just like a car. That is what the pcv Valve in car is for reburning the crancase blowbuy vapors. But it would have to have a check valve just like a car. Look up PCV Valve for more information on this. the new OS 4 stroke Engines reburn the crancase vapors from what i have heard, havent read up on it.
Best thing to do is just vent it to a tank with a vent on the tank if you want to catch all the excess oil. or just vent it to the outside of the plane and after flying wipe the plane off like i do. Keeps my front wheel on my trainer nice and lubricated.
But connecting it the the muffler would be asking for trouble dont do it.