From what I can gather from some online research, it's actually quite hard to cross the border from Haiti to the DR even if you aren't a prison escapee. Their border is actually quite secure,
That makes sense to me. Haiti is much poorer than the Dominican Republic, and it is very politically unstable. If it were easy to get to the Dominican Republic from Haiti, the DR would be overwhelmed with hundreds of thousands, if not millions, of economic and political refugees.