Now that my curiosity is up, I went over to plowsite.com (big plow guys tech site) to search for airbag deployment reports. I found ONE, but it's pretty credible. Guy posted a picture. He had an F-150 with a Boss V plow on it (Really? A V plow on a 150? lol) and he hit a water meter box and his airbags deployed. However he didn't say how fast he was going...
As one commenter says:
So I guess I retract my statement that it is IMPOSSIBLE to set off airbags from plowing. But I stand by my original statement that if you DO set off your airbags, you were probably going too fast
As far as the air bag, that would make sense. If you hit something solid going fast enough, it shouldn't matter if you have a plow in front of you or not. If the vehicle comes to a stop fast enough, it should deploy the air bags.