Yes, although you'll have to do the actual tooltip drawing with some custom code. Try this:
1. Set NodeXLControl.ShowVertexToolTips to false. That will turn off the built-in tooltip drawing.
2. Handle the VertexMouseHover event. In your event handler, read the SelectedVertices property. Create a Visual object for each selected vertex and draw the Visual objects on top of the NodeXLControl, using Vertex.Location to place them.
There are several ways to draw them. You can add them to the container that contains the NodeXLControl, making sure to give the Visual objects a higher Z-order than the NodeXLControl, or you can use NodeXLControl.GraphDrawer.AddVisualOnTopOfGraph()
to let the NodeXLControl do the work.
3. Handle the VertexMouseLeave event. In your event handler, remove your tooltips. If you used NodeXLControl.GraphDrawer.AddVisualOnTopOfGraph() to draw them, use NodeXLControl.GraphDrawer.RemoveVisualFromTopOfGraph() to remove them.
I haven't actually tried this. It's sort of an unusual requirement.