What for? No, the raytrace 3D stuff requires NVidia. Yes, pretty much every other standard OpenGL hardware acceleration feature will work with ATI as well.
This page includes a list of graphics cards that After Effects supports for ray-traced rendering.
Anyway, I'm just saying this to back Mylenium up with proper sources. In After Effects, other cards work for most anything else other than the 3d ray-traced rendering.
As the others have said, the ray-traced 3D GPU acceleration requires an Nvidia card, but that is the only feature that does. That is a very important point.
See this page for details: