If someone is from a restricted country using a VPN, they better be careful because Duelbits could ask or ask them to do KYC. And Duelbits may immediately block your account because you come from a restricted country or a country on its block list.
Many reasons to trigger a platform tool to freeze/ block an account and it does not need to relate to compliance problems but also can be related to security issues.
If you don't break the platform's Terms of Service, you can submit documents or information to unfreeze your account. If a platform is legit, they will not permanently terminate your account because of VPN. If they do this, they should have more reasons for such serious termination.
Duelbits certainly wants to avoid getting in trouble by still allowing those from restricted countries to play in its casino. But it's best not to use a VPN if you can access Duelbits or another casino so that it doesn't cause problems. Or you can use a premium VPN to access casino sites.
They accept VPN and even allow users to change usernames but prevention is better than cure and if you can use their service without VPN, why do you need VPN and use it if you are aware that VPN can cause some kind of troubles in future?