Do morally good speakers exist? 

Idea to have morally good orators is a very good idea. Thus ability to speak publically would be considered not just as ability or set of skills, but as privilege. I wish that every speaker in our world would be morally good, but it is IMPOSSIBLE.  From historical prospective we find that successful and persuasive speakers were not always ethical. No need to mention, Osama bin Laden, Hitler, Stalin and many others were great orators, but yet unmoral people. Immorality of some of those is unquestionable, when others from certain angle can be justified as ethical. 

It depends on what kind of ethic you rely on. For example, from Muslim prospective, Osama bin Laden was acting ethically in accordance of Islamic morality, when western people can say, that his deeds were completely immoral. Thus we can conclude that phrase “ethical orator” is subjective. Even within the same country understanding of morality can vary significantly. For example, on one hand, there are speakers, who support, practice and justify homosexual relationships, thus saying that it is morally good, on the other hand, there are orators who claim that such kind of relationships are completely immoral. 

This case demonstrates us that we have to rely on the same ethical concept and follow the same moral rule in order to require some kind of morality from speakers. 
Honestly speaking, I would really love to have all speakers to be ethical, according to my understanding of ethic, but we live in a free country and each of us understand it differently.