I highly doubt there’s a direct way to use WPO to influence Niagara sims, as WPO is only a part of the shader rendering pipeline and is not part of any actual gameplay or collision rendering (this is the same reason you can very easily write to shaders but it’s very very difficult to read any info from shaders).
I would recommend using a proxy mesh with Render in Main Pass and Render in Depth Pass turned off. This will still serve as a mesh for gameplay purposes, but won’t be physically rendered. While the shape may not be exact, it should be close enough to sell the effect.