Bunjevci are croatized in second half 19th and first half of 20th century. When they together with Orthodox Serbs settled in Krajina and Dalmatia they were not Croatians.
Milutin Dedić (brother of Arsen Dedić) about origin of Krka Bunjevci 28:29-30:20
https://youtu.be/oo1U2I3Vs5c?t=1709
Some Serbian Orthodox families carry clade of I2-PH908 which is marked as "Bunjevac" cluster, such as Došen from Lika, Polić from Bosanska Krajina, Ivančević from Kordun, Odobašić from Slavonski Brod etc. Their lines originated from western Herzegovina, once western Herzegovina was Serbian land.