Hi Russ,
I've never tried this but my instincts (along with being an electronics engineer) tell me that it probably wouldn't be a good idea.
The DMX Wiki
http://en.wikipedia.org/wiki/DMX512-A has this to say:
"Cabling for DMX512 was removed from the standard and a separate cabling standards project was started in 2004.
Two cabling standards have been developed, one for portable DMX512 cables and one for permanent installations. This resolved previous issues arising from the differing needs of cables used in touring shows versus cables used for permanent infrastructure.
In addition, cable performance is now specified with regard to nominal impedance and capacitance to provide guidance as to what constitutes an acceptable cable.
For example, microphone and line level audio cables do not have the correct characteristics and should never be used for DMX512. The significantly lower nominal impedance and significantly higher capacitance of these cables distort the DMX512 data which can cause irregular operation or intermittent errors that are difficult to identify and correct."
Actually, my concerns were more to do with bleed of the 250kHz RS485 signals into the audio signals, and safety concerns as the lighting controllers may be on different phases of the mains supply from the audio systems
So I guess that's a 'No', then
Steve Smith