Yeah a breather on the valve cover is just fine. The amount of air drawn into the crankcase during idle is such a small amount it really has no affect on idle quality when in blowthrough. When out of vac, the breather now vents any blowby which doesnt need to be recirculated. Yes it was once metered air but made it past the rings. Doesnt mean it needs to be recirculated.
Ive had nothing but success running blowthrough setups and putting a breather on the valve cover. Much less hoses, no issues running open bov, its really a win win situation. Also noticed a much quicker response as well. A/f one vs the other was almost identical.