Heres a good explanation about the Covenant races, for those who have not read the extended universe such as the books/comics the Brutes, some of them that were on other worlds or had ships they would be either mercenaries or warlords fighting amongst each other. Even if it is not mentioned in canon or in game Jul's Covenant could possibly have hired some Brute mercenaries to fight, also in Glasslands and The Thursday War there were Brutes on Sanghelios who were hired for various jobs though they did rebel they would be considered hired workers before their little rebellion. Also if you read the Kilo-Five Trilogy there were even Brutes, Grunts, and Jackals living in the Human colony of Venezia with little to no tension.
However Drones post war not sure where they would be I would assume most had gone back to their homeworld. But that's my two cents if you guys want to look up the info on wiki or read the extended universe if you have not.
