Thanks for the reply. Earlier I tried taking my UTexureRenderTarget2D and used ConstructTexture2D and a FSlateDynamicImageBrush which I add to the SWindow which does indeed work in so far as I can make images paint the SWindow. However, this method uses ReadPixels which is what I was trying to avoid. ReadPixels is a huge slowdown since we are pulling the texture from GPU, blocking the Renderer.
My understanding was that the main viewport for the game was basically an SWindow of some sort, perhaps I am wrong, I really would like to have the SWindow act as a viewport that I can paint with the TextureRenderTarget directly like how I can using AHUD and the main viewport. Really I just want to render my UTextureTargets to a viewport other than the mainviewport. Heck, the viewport does not even need to be visible so long as it exists in memory somewhere so that I can use my post processing on the FSceneViewport rendered scene.