Is it “legal” for a Senior Vice President and Provost of a College to be Intimate with a PHD Candidate in their editing? Is it “legal” for a Senior Vice President and Provost of a College to be Intimate with a PHD Candidate While working on their dissertation of the same School?
The law varies widely, but I doubt that there are many places that would have laws against this. But university regulations are a different matter. More, but not all, would have rules, usually to forbid it. It would be, in most of those cases, a violation of the VP, not the student, I think. 

But the situation can be fine, provided that the VP has no influence whatever over he grading/ranking/prospects of the student. This might be the case or not. It would probably be unethical if the student's future depends in any way on actions of the VP, rules or not. 

Whether it is wise is another matter. Reputation is important.