Not sure about the vanilla at all; I’ve never coupled it with rhubarb.
I usually stick to a bit of ginger; or maybe some cinnamon & nutmeg, with walnuts; or orange.
I used the zest & extract because I didn’t have fresh orange peel that the recipes I adapted mine from all called for.
I might go with the cinnamon & nutmeg with a touch of ginger. I just checked my recipe for the rhubarb crisp and while is uses cinnamon it didn’t call for vanilla, so I’ll leave it out. Thanks.