Yes, 3D WebView supports touchscreens on Windows! Some notes on touch support:
3D WebView's prefabs (WebViewPrefab and CanvasWebViewPrefab) detect input through Unity's event system like described in this article. Unity's StandaloneInputModule detects input from Windows touchscreens, and 3D WebView's demo scenes use StandaloneInputModule, so they work with touchscreens out-of-the-box.
The prefabs also support dragging to scroll by default, because the default value for WebViewPrefab.DragMode is DragToScroll.
The prefabs don't yet have out-of-the-box support for multitouch gestures like pinch-to-zoom, but if you need multitouch gestures, you can implement them in your app using the IWithTouch interface. I plan to update the prefabs in the future to add built-in support for multitouch gestures, and I'll update this article when I do.