Through my degree in Health Psychology I have become a little familiar with both of these counselor concepts.  A rehabilitation Psychologist is mainly focused with helping a person of any age who may have a disability to come to terms with their disability and helping them determine a path to independent freedom to over come their disability and have a better life.  A rehabilitation psychologist would not generally assist a person with a terminal illness aside from helping them find ways to live better.  In the hospital setting, talking to a person with a terminal illness would be best using a counseling psychologist.  The counseling psychologist will help this person with coping skills and helping them come to terms with their illness, but also helping them to understand that their life does not have to end in a traumatic way.