Using cat5 and mic cables within same DMX512 universe
CAT 5 is acceptable, but how it will interact with the rest of the mic cable (Generally about 60 ohms differential or so) is a bit anyones guess, but it will not likely make things better, especially as I suspect you also don't terminate, and some of that kit may or may not be using proper RS485 line RXs? 

For me, doing this with mic cable rates an invitation to Murphy, who as we all know is always watching. IME it is the sort of thing that typically works just fine until the audience comes in, at which point you loose control of the blinders and strobes... 

If I had to go here for some reason I would use mic cable for the extension, simply because it avoids an extra impedance discontinuity, and I would terminate with something closer to 60 ohms then the usual 110, to match what most mic cable tends to be, but there is a reason most of my 'mic cable' stock is actually 110 ohm AES digital audio cable (Which handles DMX just fine). 

End of the day you are looking at ~30m of cable total which is a very short run as these things are measured, but you are operating well outside the defined standard, so no guarantees of anything much.