For now, you can consider it the same model. And keep in mind, the only thing that matters is your final export in your render engine. So reapplying smoothing in maya is something you can do at any point. It doesn't matter then if zbrush isn't recognizing it. But to understand what is happening, you need to study…
A little more explanation on what Zbrush is doing: Zbrush doesn't render 3d models the same way a program like Maya does. This is because zbrush isn't a full 3d environment that has cameras or lights physically positioned around the model to work with. It's just a model floating above a static 2d painting canvas. When you…