The official languages of Haiti are French and Haitian Creole (Kreyòl Ayisien), which is a French-based creole language, with 92% of the vocabulary being derived from French and the rest primarily from African languages. Haitian Creole is the native language of the masses, while French is the administrative language, even though only 15 % of Haitians can speak it and only about 2% can speak it well.
Creole is mutually intelligible with French on the most basic level, so the competent French speaker should be fine in limited circumstances. Many Haitians are very appreciative if you take the trouble to learn a little bit of one of the official languages (preferably Creole), rather than using an interpreter or expecting them to speak English. Haitians working in tourist areas usually speak English well enough for conversation.