"I learned from another responder that the spelling is Rajkovic and it is Croatian name. "
Original spelling is RAJKOVIĆ.
It was present in that area among ethnic Croats and ethnic Serbs at the time you are researching - labeling it as *Croatian* surname is thus pointless, incorrect and rather ignorant of the facts. :)
If your ancestors RAJKOVIĆ from this area were Roman Catholic they were Croatian.
*Name* or all RAJKOVIĆ families who lived there were not.
att: detailed info on not-Croatian RAJKOVIĆ nobility XVIII century, Vojvodina
Serbian Genealogy Society SGS " Rodoslovlje" http://www.rodoslovlje.com/en