Nope. The drag knife is built to rotate freely. The gcode has to incorporate that though. As far as I understand that the knife is put into the material so the tip barely goes in, then the router moves it into one direction so the knife turns around before being pushed into the material.
Youtube has a few videos on how drag knifes work.
Donek Tools sells a drag knife:
He also describes how to use it:
And here is one who built his own:
I've ordered the plans by "buying him a beer", but didn't get them yet. Which isn't too bad, because I don't even have a router yet :-D