We have a floating pane on our app that contains a QML WebView that can be moved around the screen and resized. When the pane overlaps a part of the app that has a DragHandler and a Flickable, moving the scrollbars on the WebView propagates events to the DragHandler and Flickable behind it.
The attached project is a stripped down version of it. The blue dialog can be moved around by dragging the header. It also can be resized using the red button on the lower right. When part of it is over the column of buttons, and you scroll the WebView, the buttons move up and down. The "Swipe" text appears at the top when the overlaid item also gets the swipe event from the WebView.