1. First of all, correct expression i's not '하국사람', it's '한국사람' (한국 means Korea, and 사람 means person) 2. 한국 사람 = 한국인. It's almost same. Many Korean don't care whether you use 한국사람 or 한국인

I believe 사람 is the native Korean word, while 인 has derived from Chinese.