Yes, I wouldn't have got it if it didn't
Even before I ordered my mac I knew I would need extension cables for the ACD because I read posts on how short the monitor's cables were and also saw it in the local Apple store. I contacted Dr. Bott to confirm their mDP cable supported audio passthrough.
FWIW: I bought my Dr. Bott cables from here:
http://www.macproonline.com/Dr-Bott-Mini-DisplayPort/Displays/Accessories-for-your/-p8236146.html
I got it from Mac-Pro because (a) they were hard to get at the time (even Dr. Bott itself didn't have any, which apparently is the case even now -- just checked the 2m on their
site) and (b) I found a bunch at Mac-Pro which is fairly close to where I live. Heh, the price there now looks a buck or two cheaper then I paid at the time!
Editorial: Many of the ads for these kind of cables are, IMO, incomplete since they also come with USB. So when they advertise the cable supports audio (generally they say "Audio and video passthrough" if they say anything at all) you can't tell for sure if the mDP supports audio
in addition to the USB which of course supports audio. So what I do when faced with ambiguities is contact the manufacturers directly.
At least Monoprice, my preferred (first choice) place for ordering cables, is honest to say up front that their mDP cables don't support audio. They're a great place to order cables if the cables fulfill you needs.