Last year, one of the more sucessful undergraduates in our department was deaf. She was amazing...you wouldn't really know it unless you saw the hearing aides. She's now in graduate school in Australia and doing well, so its definitely doable.
There's a deaf woman in my undergrad department-- she has one of the highest GPAs in my major, and has been able to successfully conduct long term research, so I don't see why a deaf person couldn't get a PhD. She just has to hire an interpreter for her classes, but she lipreads better than most people hear. She's applying to grad school now.