The "real" ancestry of Hendrik Venter is unknown. Even his "real" surname is unknown at this stage. One of the ways to track the South African Venter family, is to do a DNA test. Although it might not highlight the Venter ancestry directly, it will (over time) narrow down their origins. Of course, for South Africans, it will plot you in terms of the local Venters. So far, everyone tested indicated belonging to the R1a1 Haplogroup.

 At this stage, it seems that the majority of people belonging to this Haplogroup, are of Eastern European descent:

You can view the above, dynamically, at ySearch.org.