I've seen real-time raytracers done with GPGPU solutions, but no rasterizers as far as I can remember. There's a good reason for a lack of GPGPU rasterizers though, as DX and OGL would always outperform GPGPU solutions as they can use the actual rasterizer hardware, while a GPGPU solution would need to do rasterization completely in software. Maybe there are some obscure use cases where a GPGPU rasterizer would be actually useful, but in general it'd be better to stick with libraries like DX and OGL.
Another thing I'm wondering, I've been thinking about experimenting with some rendering techniques like rasterization with gpgpu by using something like CUDA. However, I have no CUDA experience and wondering if it would be possible to do so? Could there be certain advantages over just using Dx / GL?