DarkPhysics does infact have GDK support. And just to aleviate any kind of doubt in your mind, here's what a portion of my "order hitory" looks like to show the downloads availible for Dark Physics, Dark AI, and EZ Rotate, to show you that they all have GDK support too...
The latest DarkPhysics should support CUDA, at least I keep hearing it does. I finally have a CUDA capable card but haven't tested it yet. However, I do know that the latest version runs off of nVidia's software fallback, don't know about the CUDA part though.
However, I would not recommend DarkPhysics unless you are only aiming for the right to put a PhysX logo in your game or absolutely MUST have all the complex physics stuff that you don't want to code yourself. You see, DarkPhysics is incapable of being used with timer based movement. So it's very framerate dependent. This results in unpredictable performance across a wide range of systems. There are ways to reduce it's impact, but ultimately, you cannot keep the gameplay consistent between machines.
If you can muster it, would highly recommend using Sparky's Collision and from there make your own in-house physics.
You see, nVidia's PhysX system running on CUDA actually uses up video memory and can slow down the framerate. So I usually keep it turned off and let my CPU do the PhysX instead. I actually get faster performance by not using hardware accelleration for PhysX. And that's not just DarkPhysics, that's everything that's PhysX based. My CPU handles it so much better than my 9800GTX+
Everything I needed to know about trigonometry, I learned by becoming a game programmer.
