Umm.... that depends on your definition of "compatible" in this sense.
DarkSound is probably just a lot of sound files, that should be fully possible to use with FPSC.
DarkVoices is a DBP plugin, so it is most likely not compatible with FPSC*.
DarkMatter is a set of models. They might be used by FPSC, but I believe you cannot use the characters etc. as they probably have different animation sets (lacks certain animations used by FPSC etc.).
Finally, DarkBasic is a programming language and was in fact used to write FPSC (both the editor and engine). You can download the FPSC source code and thus tweak it using DarkBASIC (Pro, not Classic). Thus, you can alter it to incooperate any of the Dark packages, but that will be hard work. (Yep, you'll have to learn how to program, and then get familiar with the tens of thousand of lines that makes up the FPSC source code, and still so it isn't going to be all that easy. It will definitively take time!).
So, the short answer is, for the most of them, no.
The truth is yes to all. But it will be a long way before you get to the point that your programming skills will allow you to do that. That is, assuming you have never programmed before, otherwise it's just a quick ordeal of learning the DBP syntax and commands.
Hope that was somewhat clear; the lunch is more or less burning on the stove, so parts of this message was stressed together.
