If you read this you'll note that this emulator has several rendering options, the LEAST efficient is a software mode using the CPU mainly, so yeah it does use the graphics card.
However with emulators it's possible that some cards work better than others so maybe some research is in order?
I don't know much about it, but I agree that the HD6770 is probably the best card for that price. I tried emulation once and gave up. At the time I could buy a PS2 with controller and lots of games for $100.