It is not good to use VPN on gambling a site, it brings suspicion and can lead to the gambling site to scam even people from the countries that are allowed. That does not mean Bitstarzis not a scam site though.
I get your point. Although if the casino detect someone is from for prohibited country by IP, they should've put some effort to stop user from register or make a bet. Otherwise, i would see it as tactic to get steal money from user who don't want to perform KYC verification.
They only say it's not forbidden though. They also give vague answer what would happen if you use VPN.