Anyway, one of the reasons I thought this style of gameplay would be good to implement was, as well as obviously being tremendous fun to play, it'd also allow a much better experience of playing as the Combine than other mods have been able to produce so far. Presumably playing the rebel side will be pretty similar to the general HL2 experience (only cooperative), but playing the Overwatch side I think offers a chance to implement a completely different mood to the one we're familiar with, and generally make you feel like you are the Universal Union. I've played several mods that put you on the Combine side, and none of them really seemed to capture that feel; you generally seemed like Gordon Freeman dressed up in an Overwatch uniform, sometimes with special weapons. The Overwatch Mod will obviously be quite different to these as you control lots of Combine units rather than one guy, which will definitely help prevent this familiar feeling, but it'd also be nice to keep things as Combine-like as possible when playing, and keep to the quite detailed canon that Valve created for them.
One of the things that I think will really help in this aspect is the use of Combine terminology. I haven't really seen any of this in other Combine-playing mods, where they all tend to either speak normally/cornily or use generic military terminology, as well as use specifically Resistance slang (thumpers, manhacks etc.), when in fact the Combine have a well developed way of speaking and some very specific terms for different things. For me, not including any of this rather ruins the feel of becoming the Combine, goes against the Half-Life 2 canon, and generally makes it feel less like a polished game that meshes with the storyline. So yeah, if possible, I'd like to see as much of the terminology used by the Combine as possible, whether that be for the UI or announcements or whatever. This would make it seem more in-keeping with the HL2 canon, as well as keeping it even more distinct from the Resistance side as well as similar factions in other RTS games.
The Combine use language that is often euphemistic and based in medical terminology. Some things haven't yet been given a designation (e.g. Striders) so you may have to invent an appropriate term for them, and some, such as Advisors, seem to be referred to the same by both factions. I also have to stress that the use of the word "Combine" appears to be more of an abrasive slang term rather than their official name, so if possible the Overwatch shouldn't make reference to that name, instead substituting "Universal Union" in its place. Several mods have them referring to themselves as Combine, and it annoys me.
Regardless, here's the terms that I've been able to gather from various in-game sources (mostly sound files or the sentences.txt file within scripts). Ones in bold are pretty much for definite, whereas ones in italic are inferred.
Anticitizen 1 : Gordon Freeman
Airwatch : Scanner Network / Hunter Choppers / Gunships
Biotic : Antlion (Could also possibly also refer to other Xen creatures)
Bodypack : Armour
Boomer : Gunship (?)
Bouncer : Enemy Grenade (Zombines use this for their own grenades, but they're malfunctioning, so it's not that surprising.)
Cauterize : Cut Off / Kill
Containment Field : Shield
Control Section : Citadel
Dislocate : Remove
Displace : Retreat
Deserviced / Duty Vacated : Dead (Usually used for friendlies)
Exogen : Hostile Creature/Object (Usually used to refer to Antlions, but also occasionally to other hazards such as reprogrammed Sentry Turrets and Rollermines.)
Expunge : Kill
Extractor : Friendly Grenade
Flare : Grenade (In general)
Ghost 2 : Gordon Freeman
Interpose : Cover
Lock : Stand Ground
Hard-Point : Mounted Gun Emplacement / Bunker
Hurricane : Key Resistance Figure (Not Gordon. Used to define status of "outbreak")
Necrotic : Zombie
Noncitizen : Rebel
Outbreak : Human Revolt (When said three times in short succession, means that the speaker is overwhelmed.)
Parasite / Parasitic: Headcrab
Phantom : Gordon Freeman
Political Conscript : Stalker (?)
Priority 1 Objective / Primary Target : Gordon Freeman
Priority 2 Escapee: Other Key Resistance Figure
Probe : Investigate
Prosecute : Assault
Protection Team: Metrocop Squad
Restrictor : Thumper
Ripcord : Retreat
Scalpel : Overwatch Sniper
Signature Imprint : Data Packet (Presumably)
Stabilization Team: Overwatch Soldier Squad
Sterilize : Kill
Sterilizer : Sentry Turret
Storm System : Canal
Tag : Kill
Target 1 : Gordon Freeman
Transport : Teleporter
Universal Union : Combine
Unrest Structure : Resistance Station
Vance Prime : Eli Vance (Presumably)
Vance Sub-Prime : Alyx Vance
Viscon : Enemy Sighted
Verdict : Pistol Bullet
Virome : Antlion
Viscerator : Manhack
Workforce Intake Hub : Trainstation
10-99 : Overrun
10-108 : Friendly Dead / Death
404 : Riot
Apologies for the essay about a very nitpicky subject, but I really think it'd help to completely polish what looks to be a great game, and make it seem more "official". Feel free to discuss whether implementing this would be a good idea or not, or dispute the terms I've gathered.

tl;dr: Use Combine language in the Overwatch side.