Dnb tends to make heavy use of samples, so I suspect the artist that wrote the tune might have only used samples. If you'll give me the stream that you're listening to and the approximate time (within a few seconds) I could try to determine what the tune is you're hearing and go from there...
Also note that some of my dnb producer friends DO play their own guitars in their tunes occasionally--for example Calyx was a longtime jazz guitarist before he switched to dnb in the late 90's. Teebee used to try to work on his piano chops before he switched to dnb. etc.
The jazzy guitar starts at about 5mins in. I was listening to the first "Valis - September 22nd on Dnbradio" link and WMP reports "Valis: Kief Science presents S".
Listening to it again now! Definitely little samples to start with, but then goes into a more full-on solo at about 06:30.
I can hear the guitar work now...I *think* that's a 12" off of a label called Pivotal but I'll have to double check that when I get a chance. If you're interested in dnb keep that site I linked, it's the best online d&b database for vinyl/cd/etc releases and it's run by a rather nice chap.