well, if your Naks were using batteries, NOT, phantom power, and you didnt have the phantom power on on the ua5, then most likely, there was not any power being sent to your mics.
The sound guy does have a valid point (but is also probably not familiar with the ua5). I have heard this before. Splitting a signal from the mics before phantom power can supposedly harm the signal or mics. I have done this multiple times, however, and never had a problem.
So, you can fry your mic, but it probably wont happen!