I've recently started using the Radeon Prorender, and I tried to use a bump node for some icecream, and in Eevee and Cycles it looked how I wanted, but in Radeon Prorender it had no effect. I tried to plug it into the normal from the Principled BSDF and the RPR Uber, and I tried the displacement from the material output, even with other nodes like displacement or normal. I can't get it to work, and the bump is really important for the render.
So, after having similar problems, I realized that in the Prorender materials library they have their own RPR bump maps, RPR image maps, RPR normal maps and so forth...
But there doesn't seem to be a way to add any of those through the Add Shader menu.
So I've been copying the needed nodes from their prebuilt materials library. Not sure why we can't add those in the add menu.
Some nodes seem to have some cross compatibility. From what I can tell the mix shader and RGB mixer both work.