It's not going to happen since the Union of Nations comes first, and the USJ is a central member. Once Lelouch retakes Japan by beating Schneizel, they basically have no choice.
Ohgi might betray when he finds out about -
1. Zero killed the Japanese Liberation Front.
2. Zero instigated the whole Euphemia massacre event.
3. Zero has an evil eye he uses to control people.
4. Zero is an insane, rogue Britannian Prince.
5. Zero held Viletta captive within her own stronghold for months on end, tortured by fear of getting found out while forcing her to be his slave.