There has to be some sort of balance in knowing the private hobbies of the person and their respective interests to the company.
Regardless, I think companies should not mandatorily infringe the privacy of their employees just because they gamble. Even if they have such hobbies but they still meet the expectations of the company, then I see no reason for these employers to screen their applicants. This should only be done if their output is hindered due to the intense and extreme causes of gambling addiction.
As much as this is favourable to the employee, employers should not screen but rather promote a healthy workspace that encourages different lifestyles. They should, in no case, meddle with their private affairs.
In most cases, company that have a strict background checking will be asking for this kind of information but like you I also don't agree
that employee should be asked regarding to this kind of private information, sort of hobby or a part of being entertained. If the person still meets the qualification, just allow him to fill the position and let him do his work.
Personal life should be taken a part from the business side, interfere only if there's already a problem that occurs which affecting the employee functionally around the company.
otherwise, if he's not being affected, then let him do whatever he wants he deserve the salary and it's on him to where to take it.