Currently, no, DarkGDK.NET will not work with Silverlight. Just as XNA and Managed DirectX will not work with Silverlight. Currently there is no (3D) hardware acceleration support in Silverlight.
However, a new release of Silverlight scheduled for winter 2008, will have support for (3D) hardware acceleration, or at least it's on the list of planned supported features. If this is the case Managed DirectX and XNA will work with Silverlight provided the right runtimes are provided.
As for weather DarkGDK.NET will work with this coming release, I've no idea. I would assume it would, provided the right runtime is available. That really depends on how Silverlight supports windowing hooks. Theoretically (and as a guesstimate I might add), it should be as simple as passing the correct window handle to the DarkGDK.
We'll just have to wait impatiently until then.
-Piro