I just spent another half hour researching this... apparently plenty of people are using it as a replacement and at one point the older Mobil 1 bottles said it was backwards compatible, but now it does not and GM has never officially stated that it supersedes DexVI.
So I will probably continue to use full synthetic Valvoline DexVI until Mobil 1 or GM state that LV HP ATF supersedes DexVI.
So I will probably continue to use full synthetic Valvoline DexVI until Mobil 1 or GM state that LV HP ATF supersedes DexVI.