You posted that in Islamic religion, gambling and betting are seen as Haram. Gambling sites also know this and they avoid to relate with Muslim's festive celebrations. Or am I not getting it right? I have not noticed anything like that before.
Christmas and the Easter celebrations are symbolic for the birth and death of Christ, the Casino's know this, and are also aware that gambling is a sin in the religion of Christians, but they still do not fail to bring up Christmas and Easter events. Are you saying that Casino's are religion sensitive?
Here in Spain, a historically very Christian country but where most people is non-practicing nowadays, we have a special Christmas lottery hosted by the government where
more than 70% of the adult population participates, an unthinkable percentage in any other game by far.
Following this logic, I guess that depending on the religious orthodoxy in each country, casinos would take a different approach when it comes to gambling during Ramadan. For example in Turkey where most muslims are non-practicing afaik I think that there would be little problem with that, so we cannot find a categorical answer to the OP's question.