If you don’t mount it behind the windscreen then you don’t need the filter since there are no reflections, even if you do mount it behind a bike windscreen, it is unlikely to work well due to the shape of the glass.
If you want to make a high quality movie then you might want to rig one up anyway since it will improve the road surface, colours, and maybe the sky, but it will not be an advantage for use as an accident camera.