At least, he can ask the support system if their site allows using VPN and will not have a problem cash out the win money if he wins. By doing that, he can get the right answer from them to decide whether to use VPN or search for other reputable gambling sites. But move on to the other gambling site that does not require too many things will be better if he does not have any problems in the future. Many gambling sites are out there or from this forum so he does not have to feel difficult to search for the right site.
That ok if the site support gives go-ahead for the use of VPN, my fear is if the site will allow VPN them what is the motive of setting restrictions in place. Why I said so is because of my experience my account got ban for using VPN despite the support clearing me to use it.
What I am worried if when the support sites allow using VPN when we win and want to withdraw the money, they will ask to do KYC, no matter how much they win money. That is a bit scary, you know, that will not be okay if they do that because they do not tell us that we must verify our account to withdraw the money. Hopefully, that is not happening in any gambling site and it is better to explain in the beginning than we should face that problem in the future.