Hi Esteban, i am native french speaker and i am currently living in Africa. The biggest communication issue i have with the people here is the accent, definitely. They have a lot of accent from my point of view, so it's hard for me to understand what they say, and when i talk, they ask me to repeat many times too. The grammar or the vocabulary doesn't change much, they of course have some "african" words but the difference is more the way the sentences are built, or the metaphors etc. They will use examples or proverbs you don't know because they don't picture the world exactly the same way.
Hm, last thing, they usually speak slower than french people because most of them have local languages as mother tongues, it helps. It actually really depends on the place you will be or the people you will talk with. For example im working with NGOs in rural zones with low development level, and there are no dentist, so many of the old people (+50 y/o) have bad teeth and are harder to understand, plus many of them didn't reach secondary school because they are farmers and also french is clearly not their mother tongue, so sometimes it can be very hard. Now if you go to a big city it's really different.
I read once a survey that was led by a teacher in some east african university. He asked his students to find whether in an audio it was a french or an african. The answers were all the same, they say the french man speaks faster, the idea is clearer, the vocabulary is deeper, and they say the way he speaks looks easy (like, no effort). On the contrary, the african speakers look like they struggle more while talking, many words were useless in the sentence etc. No judgement tho, many of them have french as a mother tongue and speak way better than many of the french people.
Regarding Haiti, i have no idea, i have never been there.