Applicability of HMA on Tribal Community

Sir, my friend belongs to schedule tribe. He got married in 2011. His marriage was without taking dowry. His wife started to create nuisance and problems in his family, like senseless fights with husband, relatives & in-laws. She has been living with her parents for last 3 years. In the mean while, she filed complaints against him, his parents n relatives in police station like under section 406. Later the police after investigation found that the alleged complaints were false and filed just to harass my friend and his relatives. My friend n his relatives did their best to reconciliation between him n his wife, but all in vain. Since my belongs to ST community and he can't go for divorce under Hindu Marriage Act, he went to his community elders as per custom prevailed in his community. After hearing from both sides n making numerous failed attempt for reconciliation, elders decided for divorce. They gave their decision in written to my friend. This happened few months back. He consulted few lawyers, he was informed that getting a decree of divorce from the court in his case is not necessary as he belongs to ST and divorce are done based on their customs only. Now my queries are: (1) whether my friend has to go for any kind of decree from the court even when hindu marriage act is not applicable to him? (2) if yes, then how and what should be the approach for it? (3) if No, then what should be done so that false cases against him like dowry etc can be avoided, as the probability of filing false case by his former wife always be there. (4) whether can she file maintenance case against him even after customary divorce? (5) whether cases like dowry , domestic violence can be filed after divorce? Sorry for the long list of queries. I have to ask these queries as my friend has been receiving threats from his former in-laws n wife of various cases & due to this he is mentally very disturbed & depressed. He already suffered alot since his marriage. Please advise over the queries above at the earliest. Thanks.