I think you can use NVidia.. but you'll want to also try RenderMonkey.. and note... each I THINK makes HSDL (name of the "language" shaders are written in.. kinda C++ and Assembly language'ish ...
The trick is you need to know enough about HSDL to debug and tweak the shaders you make so they "work" in DarkGDK.. its not that DarkGDK is overly tempermental... you just want the shader to be able to talk to DarkGDK and vice versa... so sometimes variable names matter etc.
That's all I can tell you. ... though you will want to scope out the DBPro forum on shaders as there are many... AWESOME threads on it and the same stuff they do to get shaders working in DBPro applies here.