I've had issues with the AMD-GPU Pro driver with this game.
I'm not sure what the issue was, and since the Open Source driver runs better with my particular (manufacturer/model) card due to the Open Source driver having better power management (I'm as surprised as anyone else on this.) I decided to switch to the Open Source driver anyway.
If anyone else has trouble with AMD cards and the AMDGPU or FGLRX Legacy driver, I recommend simply switching to the Open Source drivers. They are already running quite well. (I do NOT recommend ever using FGLRX anymore. The Open Source drivers are better for the vast majority of cards. AMDGPU-Pro is a decent driver, is slightly faster on some bottlenecked tasks and has more OpenGL features, but is generally less compatible, less power-efficient and less stable than Mesa 12+ drivers.)