You could use a custom texture for the cursor. The following code hides the mouse cursor and adds a crosshair:
Code:
#Disable mouse navigation and hide cursor
viz.mouse.setOverride(True)
viz.mouse.setVisible(False)
#Add a crosshair that is linked to the mouse
crosshair = viz.addTexQuad(viz.ORTHO, texture=viz.add('crosshair.png'), size=64)
viz.link( viz.Mouse , crosshair, srcFlag=viz.WINDOW_PIXELS )