My questions are... Can a bettor reject being unveiled to the public? Are gambling platforms paying an extra money for the publicity?
Every gambling platform must have their own terms and conditions for such a publicity and it can be different from one to another. From player's perspective, of course all players has the right to reject the publicity because of security or privacy reason but the next question is, will be there a consequence for the player who reject the publicity? Of course it will be depending on the terms and conditions of the platforms.
If we discuss the publicity rules applied by gambling sites then it goes back to the rules of the gambling site, because actually the ones who benefit from the publicity are the gambling place or platform, they really want it to increase the number of players on their platform. Regulations regarding privacy are definitely different in each region, and I don't know how these regions regulate this privacy issue, if it has to be forced then the jackpot winner cannot refuse the publicity requirement.