They're Covenant, but they work for Jorgey. He used to hunt the Covenant forces that landed on Requiem to claim his vengeance for what they did to Reach. He later allies himself with the Covvies and uses them as his soldiers, workers and advisors. He enjoys the company of Grunts, mostly because they fear him. However, he despises Skirmishers, they are the only race in the Covenant that he truly hates. This is why there are no Skirmishers left alive by the time Johnny reaches Installation 04. Jorgey's Covenant are not to be confused with the Storm Covenant, who are esentially Covenant that still worship the Didact and the Forerunners, and when the Didact finally reveals himself, the Storm go to war with Jorgey's Covenant, along with the Prometheans. However, Jorgey has hundreds of Engineers working for him, and they are the best fighters in the Covenant army, so Jorgey completely decimates the Didact's forces and he eventually surrenders.
When Jorgey unveils his master plan, the loyal Covenant go with him to New Reach and live out their grunty lives on Sword Base Mountain. They later give their fleet to the Reachites to use, and Jorgey leaves them to wage war as they will.