That is not the reason. The reason is that wrestling is the top sport in Dagestan/Chechnya, but it isn't a top sport in the rest of Russia. Wrestling is literally the #1 sport in Dagestan/Chechnya. A quick Google search shows that in Russia as a whole, football, ice hockey, handball, basketball, futsal, boxing, auto racing, volleyball, track, boxing, tennis and others are more popular than wrestling. None of which are precursors to MMA.
There are no Dagestani's in the NHL, NBA, or on the WTA tour. This has zero to do with their religion, the same as Canada's religion has nothing to do with being great at hockey and the religion in New Zealand has nothing to do with them being amazing at rugby. And why guys who were good at BJJ did well in early MMA and were shocker, from Brazil, which had nothing to do with their strict Catholic upbringing. If Alex Ovechkin had gotten into wrestling he would have probably murked the Dagestanis, all while being haram.