The CUDA acceleration back then was limited to a few cards, but could be hacked on for some cards that had enough VRAM and cores. I don’t doubt that it showed up, but I kinda doubt it did much because CS6 is quite limited what it actually did with the GPU. Even with a supported card there were a bunch of issues so one would use software rendering anyway. Also it didn’t help with H264 encoding/decoding. Only some effects, scaling, deinterlacing etc.
CC supports hardware accelerated encoding/decoding on supported CPUs and GPUs.
If you don’t want to update Premiere then there is the free version of Resolve.