The subtitles should allow deaf players to understand what's happening in the story and at the very least they'll be able to know when one of the voices is talking. (dagersystem.com)
Still, none of it is technically necessary for deaf players to get through a level. (dagersystem.com)
However, sound is very important in Hellblade so deaf players may have more obstacles to deal with as they play the game. (dagersystem.com)