IME, not so much with Hyatt, but rather IHG or Hilton, this all depends on a number of factors. For one, there is a difference between negotiated rates at specific properties vs. (global) "chainwide discounts".

The validations of my corporate credentials that I experienced (e.g. IC Osaka, IC ANA Tokyo, IC Kuala Lumpur) were tied to me using a negotiated corporate rate for the specific property in question and the rate was much lower rate than rack rate/ best flexible type rate (e.g. 50% or more even). This usually applies at hotels that are very near our corporate offices or so.

As one of the Director of Rooms (& reservations) told me, they had just way too much booking volume for the rate versus what was predicted/ estimated in the rate agreement with our firm and they were loosing revenue that way big time. Also many of the folks using the rate didn't match the "profile" (appearance, country of origin / passport) of travellers that the hotel had experienced before and was expecting, so they started to implement tougher validations.

Being challenged on the chain wide discount rates that can hover between 12 - 25ish percent off best flex rates depending on chain, stay duration and such has been rarer on the other hand. Often those rates are similar or slightly higher than advanced purchase type rates with the benefit of being cancellable with 24/48 hrs notice, so maybe those don't hurt the hotels as much.

Lastly, as others said, it also depends on the individual companies internal policies (e.g. we can use corporate rates for personal travel as well) and whether there are restrictions in place like booking through corporate portal (e.g. Carlson Wagonlit) and such.

Anyone using it without being authorized, do so at your own risk. Especially in desirable properties in Japan I found they really cranked up validations now that travel has picked up significantly and regular rates are much higher than before COVID.