Hi -
You can export models in various formats for use with other systems like Unity. Lately there’s some work with glTF, but other formats should work too.
A lot depends on what you are trying to accomplish. SlicerVR allows you to directly interact with Slicer functionality so things like segmentation, transforms, and volume rendering are all native. Plus Slicer is fully open source so it’s possible to program anything you need. But of course it’s newer and has a smaller developer base so it’s not as polished as something like Unity.