Just like in the content of OP, I am a stake participant and I do receive my pay in my stake account but never have i used it to gamble. The thing is, I am more of a sports bettor and I'm comfortable betting in local sportsbook using fiat.
At the same time, gambling with your signature pay might force you to go against your bankroll management. Which is one mistake I wouldn't want to do.
It all depends on the gambler mindset and urge towards gambling. Some gamblers might only want to try a few game because there's funds in their account from signature campaign but will end up gambling almost everything. It all boils down to self control and discipline. I haven't participated in a signature campaign that pays directly to the casino account but I don't see it as an excuse for anyone to gamble when he does not want to.
If you gamble whenever you have money, it means that you will not be able to manage your income because you are putting gambling first in your life instead of your major responsibility. What about gamblers that keeps their weekly gambling budget in the casino account and wouldn't gamble only when they want to. Maybe, any gambler that uses his signature campaign money to gamble because he was paid directly to the casino account does not have any important thing to use the money for.