Welcome to FT, jrnlmkr, even if so far it hasn't been that friendly a welcome!

Without delving into the morality of this issue, I can say that the PH Tokyo is one of the relatively few Hyatt hotels that often asks for proof of eligibility for a corporate rate at check-in. So I'd suggest that you try this only if you are prepared to be denied, which means you would end up paying rack rate for at least one night.

I'll also add that it is virtually impossible that inappropriate use of a corporate discount rate would EVER be regarded as illegal. This is an issue in contract law and the extreme recourse is a lawsuit which would pretty much never happen in Japan where people avoid the court system whenever possible.