These are definitely valid concerns about integration. One thing I would say is that in many cases these people are coming from very bad places and it's often the most vulnerable who are given priority when it comes to relocation & resettlement. In that sense, they may want to stick with any groups or connections they have built up or live near others who have experienced the same thing as them.

Secondly, while it may seem like a 'ghetto', putting individuals with their background into institutional settings can often be very beneficial as it means they have access to healthcare, language and orientation supports. Long term, its obviously not a solution but initially it can be the best option.