Better to have it and not need it than need it and not have it.
Personally, I use the my zoom lens quite often. I always take it with me to the parks and at times I'll use it as my "walk around" lens. My suggestion is to take both and use them both. The 55-200mm would be great for a lot more than just the Kilimanjaro Safaris. It's a great lens for shows, especially shows like Fantasmic! and Beauty and Beast. I use it with great success on rides too, like the Jungle Cruise. It's also great for capturing "details" around the parks.