Do the sounds actually need to match in pitch? My understanding is these sounds attempt to stop your brain noticing or perhaps generating the tinnitus, rather than masking the noise with something louder (like people do with a fan or noise generators)
Most tinnitus is neurological, and not sound but the perception of sound. Reverse waveform would just make it louder. At least for tinnitus from partial hearing loss, sound therapy seems to be about training or resetting neurons so they don't perceive sound when they are not receiving normal input.