Not all Krajina Serbs originated from eastern Herzegovina. But it seems eastern Herzegovinians were dominant on some way, because dialect of vast majority of Krajina Serbs originated from eastern Herzegovina.
Printable View
Map of medieval Herzegovinian clans Attachment 107363
We already have genetically confirmed descendants of Predojevići, Nikšići, Drobnjaci, Mirilovići, Banjani, Maleševci (they lived between Bileća and Trebinje), Ugarci-Dubravčići (from Trebinje-Ljubomir) among Krajina Serbs. I thinks also Burmazi have descendants among Krajina Serbs (it's not officially for now).
Borjan family from northern Dalmatia might be connected with Borjani Herzegovian medieval clan (Borjan from Kričke near Drniš is tested as I2-Y3120). Milan Borjan originated from Kričke https://en.wikipedia.org/wiki/Milan_Borjan
We also have toponyms from Herzegovina on my island (including island name), from Mostar/Čapljina area. Toponyms are almost entirely Slavic, often referring to Slavic deities like Veles.
Recently is published result of Serb with surname Krasić who is from here https://en.wikipedia.org/wiki/Šeškovci
He is I2-PH908 and it's close to Dalmatian Croatian guy Akmadžić and to several Bunjevci (Jurić, Dragičević, Rukavina etc) who are Y144305 sub-branch.