I was nervous about this too, but it has worked for me. I have only tried it when the government rate is for a state employee (as opposed to a federal gov't employee), and since as public school teachers we technically are employed/licensed by the state, it doesn't seem to be an issue. What's great about doing this is sometimes gov't rates are significantly cheaper!
I haven't been asked for an ID yet, but I keep my school ID w/ me anyway, so I am sure that will work if asked.