Tyrannies need money like everyone else. They need lots of minions to do their dirty work. A Castro, a Hitler, a Saddam, cannot tyranize a whole country. They need lots of helpers to do their evil deeds and keep the population under control. These people have to be well rewarded otherwise the regime colapses. Without money these people cannot be kept happy. It is no coincidence that when the Soviet Union fell, they were unable to even pay their soldiers. Any money going to such a regime will first be used to reward the oppressors, not the oppressed.
Excellent points.