The particular tradition here--forced marriage to the rapist--is local, sure. But like this, or stoning rape victims in Afghanistan, it's a way of dealing with an unpleasant conundrum that Sharia law does create. Sharia law DOES require the testimony of two or four (I forget which) eyewitnesses who are men in good standing in the community to convict someone of a crime. And women's word IS worth 0.5 men's word. And adultery IS a crime.
So a woman who accuses a man of rape admits the crime of adultery, but essentially can never meet the burden of proof to convict the man of rape. So long as Sharia courts are still used for criminal prosecution, there's no justice for rape victims. The exact injustice forced upon them varies from local population to local population, but so long as Sharia courts are being used to adjudicate crime, there's no justice for rape victims.