Is it must to be well conversant in Arabic to do job in Arabic speaking and Middle East countries?

No ,not required much. There are miultiple nationalities in all the Gulf countries.Local people speak English, tendency to learn English by locals is there much. Government and Organisation also give training to locals to learn English.As we interact with them, we also learn working knowledge of Arabic. Above all , the support of locals in the communication process is enormous. I spent6.5 years happily successfully  in difficult deserts also with locals in Internal Audit in Oman and KSA.