The only tool that does not work with ProRender is HDRI Studio. Topcoat works especially well with the 'physically based' workflow.
Much of the functionality of HDRI Studio simply can not work with ProRender such as the way we do backgrounds, falloffs, and the way the sky gets layered. As ProRender stands right now we are not planning to support it in R19+. If it becomes more robust in the future we will reconsider. HDRI Studio continues to work with Standard and Physical Renderer.