Believe it not out of all the Factions of Galaxy Prime the Romulan Republic was not only on the friendliest of terms with the Imperium, but requested for a Planet reconstruction of the Orginal Romulus to be made inside the Imperium so that they could be a Part of it and create the Immoruti-Romulan Star Imperium. Although the merging did not take place until the 32nd century the Romulans did control a providence within the Immoruti Imperium.
Immortus Romulus as the Romulans who colonized the artifical Imperium constructed world call it in honor of the Immorti Imperium, have sworn an alliegiance to the Imperium that would not expire less the Imperium was unable to govern itself and the Tech Family was completely destroyed. The Romulans serve among the Imperium's Scientists and Serve in its Military and many have become noted Tacticians. A very well known observation is that every Imperium ship's crew is always 2-20% Romulan. This is because the Romulans serve to make sure that there are no Mutinies as they are fanactically loyal and do not partake in any rebellion against a Imperium captain unless he or she or even it, intends to harm the Imperium.
For a list of Providences, Regions, Oversectors, Sectors, and Decisectors: see page: Immoruti Imperium Influentional Empire Manifold.