I will say this. I have no idea what is considered fraus in the USA - all I will say is when I am in the USA I never use corporate codes. In Europe, it is a different matter and the law is different. If there are codes out thee which have been put into to the public domain you would alwys be insured as it is the law in all of Europe and the UK. However, this might well see you going on Avis's blacklist. If you do not have an accident you will never be uncovered - they simply could not care less. I leave it to you to judge.
I will say this as well - it they can afford to offer these rates to Corporate Customers, does it not show how Mrs Thrupenzoff here is being ripped off at regular rates?