All you have to do to add SPARK to an existing engine is to write some SPK::Renderer, these classes will use the engine primitives to draw the particles.
I have never used DarkGDK, but I have played with DarkBASIC Pro for years (before I learned C++; I'm still continuing to use it sometimes). Althought I have made some plugins for it, I had never done any rendering plugin, so you will have to search by yourself for a tutorial/asrticle/etc explaining how to write a renderer. The good news: it is possible, I've seen a lot of rendering plugins in DarkBASIC Pro
edit: Found this on the net: http://forum.thegamecreators.com/?m=forum_view&t=157049&b=22&p=0
You'll have to write a renderer using DirectX commands. There is a DirectX renderer for SPARK1 on the svn, maybe it can be a source of inspiration.