I would doubt that is the case, I seriously doubt any cop would take a taser to a gun-fight, the range is limited, it is not as accurate, limited reload speed, etc. Tasers are normally used on the level below deadly force, the same level where bean-bag shotguns, batons or certain physical attacks might be. In theory these devices shouldn't kill, but they might. Theoretically, they are used when 'this person is actively trying to hurt someone'. But some areas might have tasers on the 'person is doing stuff to not be controlled, but it shouldn't really hurt anyone (running, balling themselves up, etc)' level.
BTW being tased isn't a big deal, it is not like on TV, after the 5 seconds, you are fine, you can hop right back up. That is the problem, a taser is a 'pain-compliance' tool, like pressure points, if someone wants to they can go right back to fighting, or at least resisting right after the 5 seconds, so the cop will use it again, etc. That is how you get stories of cops tasing someone 15 times, because (in theory) the person continued to resist 14 times.