On any dual extruder with fixed nozzles, the two nozzles need to be at exactly the same height above the bed / part so that the inactive nozzle doesn’t collide with the bed / part while the active nozzle is laying down a new layer.
The design of the Dual Extruder V3 is rigid enough and the two nozzles are close enough together that once leveled (at the factory), there is almost no chance that they will not be level when installed on the printer.
This assumes that the mounting plate on the printer is level when the Dual Extruder V3 is installed. On my TAZ 6, it was not. All I needed to do was loosen the screws holding the bottom plate and tighten them. My V3 has remained level through numerous tool head changes since then.
I believe that if the nozzles are changed or removed to clean a nasty clog, care must be taken to make sure they are still level after installation.