Yes, the zero or definite article would imply "the only one", with the indefinite article indicating "one of a number" :
Michael E. Chernew, PhD is a Professor of Health Care Policy in the Department of Health Care Policy at Harvard Medical School.
Mary Beard is a Professor of Classics.
Thomas C. Foster is a professor of English at the University of Michigan-Flint,
As for being a blessing - tell that to my students
