Vinny did not visit the city of Transylvito until after his 200th turn, suggesting that Don did not originally regard him as vitally important. At some point, Don apparently realized that Vinny had some talent for diplomacy. (The two assignments we know Don has given to Vinny were to work with the Royal Crown Coalition, and to act as liaison with Queen Jillian. Both positions require diplomatic as well as military skills.) Don had a high enough opinion of Vinny to listen to his claim that Jillian knew where Stanley was going, but he also gave Chief Warlord Caesar orders which he did not share with Vinny.
Don's recent reappraisal of the importance of Royalty has probably raised Vinny's status somewhat. He is a Count, which means that, in terms of his position in the nobility, he outranks Viscount Caesar.