I've never tried this. It seems logical that if you can hack an enemy turret you can hack an enemy firebase.
I think the FB might be a special case as I believe it takes damage as if it were a Pro instead of a Turret
Unfortunately, all it takes is a quick airstrike to get rid of that problem, unlike a turret. Supports should be able to hack Gunners. Now that's teamwork.
Then Gunners will complain the Deploy is even more underpowered... Gunner Deploy 3: -Adds Headshot protection -Adds Anti-Hackable armor.
Now that would be interesting if you could hack teammates Have a little .1/.2/.3 hover over their left shoulder