The only time nutrition or hydration could be omitted is if it does not produce a sustainable benefit to the person or might even endanger them or make the condition worse. IE: if a person is not able to digest or assimilate feedings via tube and becomes distended/ vomiting/ aspiration/chronic diarrhea.
IV fluids are usually tolerated well depending on the rate given- but if it would cause congestive heart failure/ pulmonary edema, any extra fluid might exacerbate the condition (mind you, this is a patient NOT responding to diuretics to begin with, and the assumption at this point is that death is imminent)
Be that as it may, dehydration is a painful and horrible death, and it happens all of the time in the name of palliative "compassion". To me there is no reason for a person to dehydrate in the final days of dying , lest the person actually die of dehydration instead of their original condition!