Yes - it is necessary.
If you are on a SWER line it is less tolerant of solar exports than the regular grid.
An export limiter ensures that no solar is exported to the grid under any circumstances. Without the export limiter, if your home is not using enough energy and the sun is shining the solar has to go somewhere and it will go into the grid. An export limiter throttles the solar panels so they don't produce too much solar.
You don’t need a seperate device though. Good modern inverters can do this export limiting at no extra cost.
As an aside, if you are export limited then batteries are more valuable to you than regular grid connect solar owners. The battery can be used to store the solar energy that would otherwise be throttled (i.e. wasted).