Eh......Breathers are nothing more than a "controlled" hole in the valve cover, with a baffle and usually some foam to keep oil from flying out....Air can go in...air can go out, no check valve. A PCV valve IS a check valve (just shake it and listen to the ball rattle). This will only let air out (for the most part) when functioning correctly.
For what it's worth, I have had 2 breathers on my race/street car for 20 years now with no leaks (4 different engines too).