If an older kohen, whom has never married or produced offspring, marries a post-menopausal Jewish woman whose first husband violated the terms of their and was granted a divorce, may he still duchan, and fulfil his other roles as a kohen being that they will never produce offspring in their union?

It is irrevelant whether they will have offspring or not. The main issue is what exactly happened regarding her first marriage. It's pretty rare that a marriage is annulled, and as you wrote, she was granted a divorce. If so, she is divorced and forbidden to a Kohen, so as long as they live together, he cannot duchan nor get the first aliya to the Torah. On the other hand, he is still a Kohen and must still not enter cemetaries.