I don’t see how Art IV, Sec 2 has any bearing here. Illinois was a free state before the Missouri Compromise (MC), so Illinois was not affected by the MC. And the State of Missouri decided that Dred Scott was a free man.
Don’t see any relevant application of Art IV, Sec 2, Cl 1 (P&I), Cl 2, or Cl 3 (escaped slave).
Having finally looked up Article IV, Sec 2 to read it for myself, I have to join those saying it doesn’t bear on Dred Scott’s case. He was not a fugitive. If the text of the section is your highest guide that should be what matters.