That's more than odd question from several perspectives.

First, and most obviously, joining the Avis Preferred program is 100% free to everyone and allows you to skip all the lines. You just show your DL to the guard at the lot exit booth. So there's no opportunity to ask you to show anything.

So I don't even understand the question, really.

Second, even if you show up at the counter -- and why would you do that? -- they still don't ask for extraneous IDs.

And third, aren't you worried at all about, you know, consequences? Such as if there's a wreck?

That's the question you should be asking.

And fourth, there's morality. But that's way, way beyond my expertise. Would this be cheating, or wrong? I have no idea.