The official answer from USITT can be found
in their FAQ, click here.
Despite the "right" answer being that you can't use microphone cable, many (maybe most?) installations do, as it's cheap, available, and some manufacturers (originally and especially Martin) put 3 pin XLRs on their kit, encouraging the use of a mic cable. Theres no doubt that for simple and smaller installations (and with reasonable cable lengths) it works perfectly well, but it does give another thing to worry about when something doesnt work right.
But really, if you're into the business of buying movers, the right cable is a trivial extra cost, and the more you daisy-chain up fixtures, the further you are pushing the edges of the spec. The right cable is the right cable.
Historic note: Martin didn't put 3 pin XLRs on their kit just to be different or awkward, they had a control protocol that predated DMX512, that also was electrically RS485, and they lucked out when DMX512 was created; they just had to change the firmware in their movers, and they were DMX512 compatible. But with the wrong connectors...
