So, we should not be shocked at this kind of thing coming from his mouth.
However, it points to something that really bothers me very often, which is the easy conflation of any other religion with "devil worship." Matthew Yglesias has more about the original legend:
The god who created the earth; who created the sun that gives us light. The god who holds up the ocean; who makes the thunder roar. Our God who has ears to hear. You who are hidden in the clouds; who watch us from where you are. You see all that the white has made us suffer. The white man’s god asks him to commit crimes. But the god within us wants to do good. Our god, who is so good, so just, He orders us to revenge our wrongs. It’s He who will direct our arms and bring us the victory. It’s He who will assist us. We all should throw away the image of the white men’s god who is so pitiless. Listen to the voice for liberty that speaks in all our hearts.
This is pretty standard stuff for any oppressed group, and no rational person would assume that the god of the slaves was just the devil. But that is the way any evangelical must view all other religions (or even odder sects of your own religion). However, any real analysis of Vodou shows how ridiculous it is. I wish more people would study the actual content of other religions, rather than just making things up about them.
Vodou is a syncretism of Roman Catholicism and various indigenous African religions, and acknowledges the power of the ultimate God, Bon Dieu, with the various "gods" (loa) of Vodou really being more like Catholic saints, in that they report to Bon Dieu and have provenance over smaller parts of the cosmos.
Theologically, unless you are willing to call Catholics devil-worshipers (which, granted, many evangelicals are willing to do, but I've not heard that from Robertson yet), there is no real basis for calling Vodou practitioners devil-worshipers. (It should also be noted that in even the versions of the story in which it is the Christian Devil who is promised Haiti, it is only for 200 years, which has already expired.)
Again, this being Pat Robertson, we shouldn't be surprised. In fact, it's likely just an attempt to get people to talk about him. But this strain of religious bigotry needs to be seen and confronted any time it rears its head.
UPDATE: The Haitian ambassador has responded to Pat Robertson's remarks (clip from the Rachel Maddow show).