Yes, it is. But we are okay if the KYC is limited for those who win for more than some amount because we know that some casinos apply limitations for withdrawal.
If someone passes the limit, he should verify his account by filling out the KYC to withdraw his money.
The KYC's purpose is to help the casino know if their members will not use the money from the illegal activity.
Before we want to use VPN, we can ask them to make sure if using VPN is allowed so we do not break any rules.
Some casinos will not have a problem using VPN as long as we do not break the other rules.
Unfortunately, that's one of the issues when withdrawing a huge amount, most casinos don't state any limit on when they'll carry out KYC unlike in exchanges where they show you the exact limits.
For the case of using VPN I think nearly all casinos don't recommend us to use it knowing it could easily break one of their terms and conditions. On the other hand not all casinos are strict when it comes to using VPN even if it's in their terms and conditions there are gamblers who get away with using VPN for several months or even longer.