Although I have some albums where I hear the tape hiss in addition / separately from groove noise, so I'm not sure if they're purely additive, as opposed to occupying different spectra.
But during a lot of genres of music, it (groove noise / tape hiss) can also be buried by masking effects of the music itself.
Spectra, along with phase, determine the extent to which groove noise and tape hiss are additive, subtractive, or neither ("neither" meaning they are distinguishable as two separate sounds, which is not quite the same thing as them being additive).
And yes, a lot of music is tremendously effective at masking noise (and modest levels of distortion for that matter).
I believe there are still actually some in-print CDs out there made from LP production masters. I agree the number of such titles is smaller than it was in the 1980s. But some CDs have never been remastered and the original 1980s masterings are still being pressed to brand new pressings to this day. In addition, for reasons I don't quite understand some titles that got remastered continued to be put out in their old, unremastered versions on new pressings in Europe for years, even decades, after the remasters came out in North America.
And finally, there are a small number, admittedly probably quite few, of brand new CD releases/masterings that use LP cutting masters because other tape sources cannot be located.