In v2.0.85 of RPR for Blender the RGB Curves Node has no effect on the output.
A secondary bug is also present in the Checker Texture Node where the resulting checkers are a very different size / scale to the Checker Node when used with Cycles or EEVEE. It would be good if RPR for Blender could apply a factor to the checker texture node automatically so that it's output better matched the Blender default.
A simple sample file is attached and screenshots are shown below for each engine.
Result in EEVEE:
Result in Cycles:
Result in RPRv2085: