This should only apply to people who have agreed to this, and should be legally treated as an issue of contracts. I believe civil courts deal with issues of contracts, so if two adults enter into a contract based on Islamic Law, Jewish Law, family tradition, or just a random mish-mash, that contract should be upheld as long as it is legally binding.

Of course religious law should not supercede criminal law, but I see no problem using it for the purpose of civil contracts.