The breathing being audible on a hot mic seems impossible in a very noisy cockpit, unless of course it is insulated by the oxygen mask.
I believe the CVR records a number of different channels. One is an open mike on the flight deck (overhead panel?) and the mike inputs to all crew positions
whether or not the intercom is in use and/or that crew position is transmitting.
Early CVRs only had an open mike on the flight deck and I believe it was the British who pioneered the hot mike system.
So in conclusion it's quite possible to hear breathing from an individual crew position.