There are no Vlachs in Bosnia, Vlach was just term used by Turks to offend Christians.
Before that term Vlach was used by the Serbs for rural people. 
All in all Serbs are native to Bosnia, for those who are not into history Ceslav’s Serbia. Croats are questionable because of many reasons, altough I am not in denial that they had some impact. But modern Croats from Bosnia are natives there I belive. Bosniaks are recently invented ethnicity and are just Serbs and perhaps to some degree Croats converted to Islam.
Knez Ivan is too biased for rational thinking, so I am expecting lol to my comment :)
If someone is propper Vlach those are some costal Croats, not Bosnian Serbs.