I pretty much agree with JSC. You could think of them in high level terms however and say they are. They both work in windows to allow games to be played on the GPUs. In that since they are the same. How the drivers work are (currently) very different seeing as AMD and Nvidia have (currently) took very different routes to get to the same place.
I say currently because AMD is supposed to bring out new cards soon which will have an architecture very similar to Nvidia's. Even when they do this however they will still check to make sure you have an AMD card in your system. The drivers are made for the cards, none others.
Thank you to for helping me out