Do you think nationality and religion can positively or negatively effect recruitment and promotions?

It should not affect it at all as it should be purely based on their skills and how they have performed against those skills.

There are challenges and those need to be openly communicated so that there is full understanding.

I think the law have put serious barriers against discrimination in hiring and the workplace so the recruiter must be ethical and avoid any  kind of this thing because he hire for the profile and the benefit of the organization

YES ! Specially in Muslims Countries in whole Gulf when Locals are less educated technically and become Sponsors to other People to boost the Business and keep their trusts on the business partners  on Religions grounds only.