How are pediatric hematologists and oncologists similiar? are they the same doctors?

Yes: Yes, they do at least 3 years of combined training in both areas.

Same: Unlike internal medicine physicians who have separate training pathways and board certifications for hematology and oncology, in pediatrics it is one training program and one board certification. Although pediatric hematologist-oncologists are trained in both, some specialize in one or the other.