It Turns out that my pc sucks at rendering Direct3D, so is there a dreamcast emulator that runs on OpenGL? (by the way, 32bit windows here)
Flycast uses OpenGL, and it has a libretro core which suggests it's designed around the Raspberry Pi. Since the Raspberry Pi didn't even have reliable support for a 64-bit OS until relatively recently, I don't think you'll have any problems W.R.T. processor architecture. Let me know how it goes! I never had any success with Dreamcast emulation on hardware weaker than a Core i5-3570K, but then again the only emulator I ever used was nullDC.