Most servers don't use these, but to me, they make the OTA whitelist more interesting.
Tasked of guarding the office of the administrator, the Sectorial Commander, or the Commander. They also guard the outskirts of any given city to scout for resistance activity. Usually these units are flagged up the most.
Standard OTA divison. They are normally the ones deployed when some sort of crises is occuring, otherwise, they are in the stasis most of the time.
Pilot hunter-choppers and gunships, again, rarely deployed. These units generally NEVER come out for any type of ground assault.
King (EOW only) Edit
This divison is for the EOW's. King's are highly trained overwatch units. They generally are the ones to lead squads of standard overwatch units (I.E Echo)
Sniper OWS. Deployed to assasinate rebel targets. Usually these units never come out, so there is really no point in having one.
Most servers use Ghost as an MPF divison, but it makes more sense with OTA. These units are deployed for stealth missions, where their deadly acuraccy and efficency are required. These units receive special training to use the Combine Sniper, along with the Ranger divison.