Thanks for the response!
Since my question, I’ve gotten an implementation of your UV suggestion working, drawing simple triangles on hit locations. However, this approach seems limited to only very simple hit marks like lines, spheres, and polygons. With my original hit material I was able to create pixel masks like splatters or smears and apply those to the hit location using world position in the material. Is there a way to create such a mask or brush in a blueprint and then render it to a target using UVs?
DrawMaterialToRenderTarget seems to suffer from the same limitation as my initial approach - the AbsoluteWorldPosition node in my MID has bogus data when drawing to the Render Target.