GrapheneOS Camera does have hardware accelerated HDR+ and Night mode along with HDRnet and EIS for videos on Pixels.
Photos in Pixel Camera look different because the HDR+ it uses by default is more aggressive resulting in higher contrast but a less natural look. Both are using HDR+ with hardware acceleration though. Videos are more similar and Night mode photos likely are too.
But I think Pixel Camera does some kind of sharpening post-processing, because I get blurry images sometimes with GrapheneOS Camera while almost never with Pixel Camera.
Photos in Pixel Camera look different because the HDR+ it uses by default is more aggressive resulting in higher contrast but a less natural look. Both are using HDR+ with hardware acceleration though. Videos are more similar and Night mode photos likely are too.