oh,
yes.
I have written and ported libraries to render text much more nicely and MUCH faster, to perform 2d operations in a db image object (so you can for example create a texture on the fly. both software library and recently a gpu based one which is hella fast) and many other little tools to help myself along the way.
of course, you can also use darkgdk with other existing libraries. For example, I use raknet for internet multiplayer coding, fmod for all my audio needs and newton game dynamics as a collision and phsyics engine.
pretty much you can do whatever you want