It might eventually be possible, but for now Slicer uses Qt 5.x and won’t port to Qt 6.x until upstream libs are all ported (VTK, PythonQt, CTK). Once that’s working you should be able to mix and match C++ code, but some parts of Slicer is in python so you might end up needing some work to make it happen.
Slicer users classic QWidget based widgets. You can mix these widgets and QML based regions in a single application.
There is also a QML-based VTK render widget, but it would take some effort to reimplement view and layout classes using this class.