Do any of them, still? DCRAW had been unmaintained for quite a while last time I checked. I mostly keep it around because of some old scripts that use it for things like... well... calibrating lens distortion. For a while now the file-level stuff in darktable has been handled by its own rawspeed module, which borrows some code from LibRaw, which was originally based on dcraw... so I guess you could say the DNA is still in there...
I think more conservative software will discard these areas as too "incomplete" to be interesting.
Yeah, for sure a certain amount of border is going to be garbage. The cases I've seen where cameras discard a surprising amount beyond that have generally been superzooms, where there seems to be a fear that one or more corners may have some hard vignetting even after distortion correction at the wide end. Given how eccentric the image circle has been on some images submitted for lens calibration, I can understand this (you can't sell consumers something that might put a little black corner on their images). In those cases, fearless users who don't mind looking at the ugly truth might be rewarded with somewhat more usable image area than they thought they had.
Another interesting case to consider is any image which is taken out of level and needs a couple degrees of rotation... this process itself loses quite a few pixels, particularly in those "possibly ugly" corners, so you might as well start with as much as possible going into it.