Technically yes. Casino don't want gamblers froma region that don't allow gambling to play on their casino because they are not allowed to. They have a license and that license is not permitting them to accomodate those gamblers. Not allowing VPN is one of the method for casino in not letting citizen from banned countries to play in their casino. Gamblers who is a live of a country that are banned from caaino like duelbits can use other casino that didn't restrict their country or those who doesn't have a license. I'm sure those casino are happiliy to accomodate them. Casinos just can't bend their license rules. Not allowing VPN is just a precaution for the casinos.
This is a matter of perspective, gamblers want to have the freedom to use a VPN as this gives them a greater degree of privacy on their minds, but at the same time casinos need to comply with the requirements of their casino license.
So it is natural casinos are not exactly friendly to the use of VPNs, as they can be used to abuse their welcome bonuses or they could allow a gambler from their list of forbidden countries to gamble on their website.