Olajuwon by couple of miles then comes Mutombo (hard to say about Russell and Wilt) Next, I would take Kareem then Zo, Eaton, Wallace, D-Robinson, Manute.....
All I know is the first and second blockshotter(Bobby Jackson~haha~ that's funny) are Rockets players
If expending energy on offense gives Hakeem extra credit, expending energy fighting the hardship in Sudan counts as extra credit. That alone he'll get top 5. If people would have mentioned the term "greatest shot blocker ever" while Hakeem was playing or made a bigger deal out of it, he'd get more credit for it I think. They threw "greatest dunker ever" at Jordan though that was debatable and not counted as a stat, why couldnt they apply that approach to Hakeem's blocked shots?
Dikembe has done a lot for his native country and Hakeem has helped him with it along with doing stuff for his country. It's not uncommon among the African players.