Well, IMO it sort of works like this . . .
Get your two kills, congratulations you are now a Star Commander . . . depending on bloodhouse, style points, and method of victory you might end up in a frontline unit (note all those factors apply to the cadet with a single kill) but the odds are not in your favor (but more than those with single kills). If you do get in a frontline unit, it will very likely NOT be the Alpha or Beta (or the equivalent for Falcon fans) as even a simple mechwarrior in that unit has more prestige than secondline/garrison Star Commanders.
If you do not end up in the frontline unit you will end up with a upper tier secondline force, something that sees action but not as much or intense as a frontline unit. This is to season the fresh sibbie officer though depending on the Galaxy Commander or Star Colonel it could be rough- thrown in with a new Star Captain (or Star Colonel) which means things could be more difficult because they are learning, or given to an old hand to keep the sibbie from getting out of control.
Just for the Wolves- an Orion IIC would not happen at this point as the new officer is still relatively untested. Orion IICs go to warriors who are about to become Star Colonels or perhaps Star Captains in Alpha/Beta when the next opening is available. Or warriors who are expected to win a bloodname with relative ease for the next open name.
Depending on the Clan & timeframe . . . not sure how many sibbie officers in secondline units would be assigned a Omni. It is less wasteful to give them to proven warriors who can get the most effectiveness out of the unit.