I have a 5700XT here in a test box. Not totally top notch, but since it basically uses the same drivers and has the same feature set as the 6000 cards, it’s still sufficient for AMD checks.
Generally vorpX is designed to be completely vendor-independent. Pretty much the only significant disadvantage when using AMD GPUs is their very basic support for resolutions larger than the monitor res. While nVidia allows to set totally arbitrary custom resolutions easily, AMD only has a few predefined 16:9 custom resolutions, which is less than ideal for vorpX. That’s something only AMD could rectify unfortunately.
Apart from that there aren’t really any significant differences with AMD GPUs.