True.
For example I1-FGC22045 and N-FGC28435 are strong in Krajina Serbs and both are founded in skeletons from Cernica near Gacko (East Herzegovina) from the late middle age
https://hercegbosna.org/forum/post1638232.html#p1638232
Krajina Serbs have tons of matches in East/Old Herzegovina among other haplos as well, and they are linguistically connected with East Herzegovina. There is no linguistic connection between Krajina Serbs and old shtokavian ijekavian ("Montenegrin"), old shtokavian ekavian of central Serbia, Torlakian etc.