MY ORIGINAL COMMENT BELOW, which is now out of date:
It does not support the ANT+ dongle via 30pin adapter. The setup seems a bit clunky and I think it is in use less and less each day, so we didn’t delay our iOS release any longer and shipped without support for it.
One option is to get an ANT+ to Bluetooth translator, such as this heart rate strap: https://www.amazon.com/4iiii-Innovations-V100-viiiiva-Monitor/dp/B00BHZQ6OG It will pick up your Vector and rebroadcast it as a bluetooth power meter.
A second option, as of yet untested by Zwift, is the NPE Cable http://store.npe-inc.com/cable-connect-ant-to-ble-use-code-handlingdisc/ which does the exact same thing. DC RainMaker talks about using Zwift with it here: https://www.dcrainmaker.com/2016/11/hands-upcoming-running.html
Finally, if there is significant demand, we may consider putting forth the effort of writing a whole new ANT+ stack to support the Wahoo ANT+ key. We would need a better understanding of just how many people own both the 30pin adapter and ANT+ dongle, and are willing to have 5cm of plastic sticking out of their iPhone or iPad.