Is it possible to fire a lock-on Rocket Launcher in "Dumbfire" mode? That is, can I fire without having locked on to something first? For example, if equipped with the NS Annihilator, and I want to shoot at a player (i.e. non-vehicle), can I? Note that I'm not specifically asking about the NS Annihilator, just using it as an example. If there are lock-on rocket launchers that can also dumbfire, please say so in your answer.
If you are specifically asking about the NS Annihilator you can't because the weapon can lock on to flying and ground vehicles. But the other lock on weaponary that let you lock on to only 1 kind flying/ground those can definitly dumbfire.
Yes and no.
Dual-lock rocket launchers (such as the NS Annihilator) can lock on to both ground and air targets. To balance this, the game was designed so that dual-lock launchers can only fire when they are locked on.
Single-lock launchers can only lock on to either ground or air targets. These rocket launchers are usually empire-specific (only able to be used by one faction). They are also able to be fired in "dumbfire" mode, which mean you can shoot without waiting for a locked-on target.
Dumbfire launchers can be fired at whatever you want to fire them at, but they are very hard to aim properly, especially if your target is moving. To compensate, dumbfire launchers do higher damage than single-lock launchers and significantly higher damage than dual-lock launchers.