If you are speaking of the surname being from what is now Austria proper then I believe you are off track with the origin of the surname.The Austria of today is mostly of Germanic roots, with the next largest population being Croats.Croats have lived in Burgenland (formerly part of NW Hungary) since the Ottoman invasion of Croatia around 1520s.Bosnia was under the rule of Austria prior to 1918.
The root of the name Pilip, which is a variant of Phillip and is found in Ruthenian and Polish areas.
FYI prior to the Ottoman invasions in 1400s the majority was as follows:
850,000-900,000 inhabitants in total Ethnical Serbs, mostly in Podrinje, about 25,000. Ortodox Wallachians in Duklja and Travunja, about 30,000. Croats-Catholics about 750,000 Croats-Krstyani about 80,000
So there is no doubt these PILIPOVIC are descended from Christians.