For professional work I wouldn't rely on it, there's no way to monitor the audio. However if you connect a pre-amp, calibrate the levels on the MKII and monitor off the pre-amp, while not ideal it would be acceptable.
I have a zoom H4n and a juicedlink, I might split the signal out of the juicedlink and send it to the H4n and the MKII. I can monitor off the H4n and I'll have a backup of my audio.
I find that going through the Juiced Link preamp with the camera gain turned way down offers really good quality sound. It sounds even better than before with the AGC disabler on.