It's impossible to have a triggerable door also be destructable. Rhino says it himself in this tutorial at the very end. Also, if it were a triggerable, the USMC could simply open the door because triggerables don't discriminate between teams.
". . . afew little notes thou:
* cant have "distructible trigger ables", so you cant have for example a door that can be destroyed, but also opened via a trigger able."
https://www.realitymod.com/forum/f189-m ... ables.html
===
For the moment, let's say those shotgun-toting bad boys just like doing things the hardcore way. Forget keys, blow down the thing with my gun!

And oddly enough, the Insurgents close doors with shovels.

===
Now, you could give the Officer a key, but it won't function exactly like one. It's a metaphor, as the game can't simulate opening doors regularly.
Let's say a key model was made, and a key weapon having similar properties to the breaching shotgun were given to it. Instead of a loud blast, it'd be a quieter metal sound. "Attack" the door knob/gate lock with this key. The door will open.
Voila! A much quieter way to get the door open. And the shovel, again, could close it, serving as another metaphor, albeit more wacky.
Now, would one Insurgent, be it an Officer or collaborator have a key that could open every door and gate lock? Are locks that simple to open with one skeleton key? We could pretend the Insurgents stole the keys from the building's owners. But a key to every door and gate lock in the city is a little quirky.
There's also the problem of these keys breaking down those destructable fences. That would be super weird to see. Unless the devs have the power to adjust what breaks what, Officers/civis could take advantage of this loophole.
"Observe, my friends, as I use this magical key to break down this metal corrugated fence!"
"Ooh!" - However, you must admit, that'd be good for laughs.
All in all, it's technically possible. I wouldn't mind seeing it either. Today, the cache hunters could just hear the blast sound, go to investigate and discover the cache. Another way to open them would be nice, to provide freedom of movement for the Insurgents to set up.
