Could a PhD degree be retracted by the institution - say, for
incompetence or misuse of the title?
It is retracted if it turns out the degree was gained by something other
than honest research (e. g. if the thesis is a plagiate). Other than that,
it varies between universities. If you dishonor the university enough, which
the university gets to define, some do threaten to retract your degree, but
that's of course a very rare occurrence and may not exist altogether in the
USA (for example). There are philosophical discussions about what an
academic degree is supposed to mean and if it should be possible to retract
it at all if it was honestly earned to begin with.
Chances are, thus, that Dr. Ross will stay Dr. Ross.