Exarch would be a better term. Strategos for ducal level titles.
Indeed. In the last days of the late Roman Empire (i.e. the Dominate) under Heraclius, what remained of the outer (western) regions of the Empire were all Exarchates. Although even the Dioceses could do. These were basically collections of smaller provinces (many equal to the size of duchies), and equal to any large medieval kingdom, without feudalism of course. The only difference was that Diocese was a fully integrated and centralized administrative unit with prefects appointed by the Emperor himself and were frequently rotated. Exarch was basically an almost-fully autonomous military governor (comparable to a vassal king) that ruled in the name of Roman Empire. He could rule his lands for life, set his own laws as long as they favoured the empire, and at least during Justinian's reconquests an Exarch was actually considered a temporary military governor until the full Diocese could be restored, which unfortunately never happened.
Now with custom titles, we can hopefully even create the Praetorian Prefectures.
Although I would love to see return of proper provincial governors and Imperial bureaucracy once you reconquer the former territory as the Eastern Roman Empire. And then once you retake the old western provinces, the same system would work there as well.