You will notice that when Harley stopped venting out the cases and just out of the heads, the cam cover is diffent and doesn't block off the lower breather section of the cam chest. I would think that if you have a case setup for breathing and one of the cam covers that does block off the lower breather section of the camchest you would have problems if you don't breathe out the case. Best to breathe out both if you have the option.
I route my case vent hose up over my transmission and down the backside. The upward slope in the hose allows the oil from the mist to drip back down into the case instead of on the floor.