Yes, you need to use the AMF/VCE encoder in OBS to use the GPU's H.264 architecture to stream.
That said, the overall consensus among streamers, is that AMD GPUs do not provide as good stream quality as Nvidia. This is because AMD's encoder support in OBS is not nearly as good as Nvidia's NVENC, and is limited to shaders.
However it's hard to get an idea of what your performance or quality will be, as it depends on the game and your settings. You will no doubt have to cap FPS to less than 60 in some games.