Depends on the take you want to have on your campaign.
Most Animals, of course, are good, but they are usable anywhere.
I would suggest looking into Atlas'
Nyambe setting book, just for examples of African legendary creatures that might be brought over (I mean, since you are already dealing with the loa/orrisha, why not the creatures as well?).
Krakens and other sea-going creatures are a must. Merpeoples of various sorts figure prominently in piratical lore. This could be extended to sahaugin and the like.
A lot of creatures from the MM are more problematic. Do you really want gnolls and the like in a setting where all characters are supposed to be human? Probably not. Same would probably be true of many "Classical Mythological" monsters -- pegasus, minotaur, etc., as they would feel out of place. Yuan-Ti could be adapted in fairly easily (fear those jungle serpents!). Don't forget plant-based creatures in a tropical environment -- lots of room for "Man Eating Plants" in such a setting!
I would suggest looking through S&SS
Creature Collections as well. The Alley Reaper, the various members of the Carnival of Shadows, the Dweller at the Crossroads, their extra Hags, the Inn-Wight, the Memory Eater, and quite probably even the Ratmen/Slitheren have a feel that fits with Things Piratical; there are also several more plant and ocean going creatures in here that could help flesh things out.
Just some initial thoughts
