is a site Ex safe, if all kind installations with various types of Ex certifications (ATEx, IECEx, NFPA, UL, Nepsi, ...) are present? is there any equivalent solution here?

the owner of site (depending country's legislation) shall decide which regulation to follow. if we consider all aspects of explosion protection (design, installation, opreation, maintenance, etc.) one regulation being followed even help to increase level of safety and more.