Hi,
I have never seen any ferrets in Mayotte and I think yours will be the first ones on the island
As for the dogs, in general, it's not a dog-friendly place because the locals don't like dogs much. They also organize clandestine dog fights. It doesn't mean though that you can't have a dog. We have a lot of friends that have one but mostly for guarding purposes.
Don't hesitate if you have other questions.
Good luck