Personally, I don't feel comfortable using a corp code that I have no right to use. I know the front desk rarely asks, but I'd hate to be that guy with no explanation when they do ask.

There are a lot of gray areas in all of our travels. The airlines and hotels have set up complicated systems and we learn to play the gray areas to our own advantage. But outright misrepresenting myself to get a better rate seems to cross the line. JMHO.