Thank you for your answer!
So, just to make sure, does this mean that every single animation has to be done with a bone setup? No bend or melt deformer or any other type of animations can be exported ?

it's too bad cause I was doing some facial animation with deformers, not bones.
Thank you for the explanation about the animation swapping, I see how it works now.
About adding vertex animations, I'd really love to do it, but I must say I've never done anything like this before. I'm a 3d artist and I have no knowledge of C++ or any of that. Is it too hard? And where do I start?
Thank you again.